I'd think the trick is, you have to bring technology that's more advanced than what the people of that time have, or what's the point?, but it can't be so far ahead that you have to build the infrastructure from scratch.
Like say you went to AD 1400 with cell phones. Of course the people there have no knowledge of electronics, or radio, or plastic, or even of electric lights. Even if you could explain to them how a cell phone works and make them understand, you have to not only teach them how to make cell phones per se, but how to make electrical wire, plastics, etc up to integrated circuit chips.
Unless you're bringing back a team of experts, you have to know all the pieces that go into whatever technology you're bringing back. Even with a year to prepare, that could be a tall order. Any given technology often builds on many other technologies. For example, I write software for a living. I like to think I'm a smart guy. If I had a little time to study and prepare, I could probably go back in time to 1920 or 1930 and teach people how to build simple computers, because most of the infrastructure is already there. But 1400? Where to start? I'd have to teach them how to make electrical wire. How do you do that? How do you make plastic? I know that integrated circuits are made from silicon and germanium. Silicon comes from sand. How do you turn sand into usable silicon? Where do you even find germanium? What does germanium ore look like? I haven't the vaguest idea. I could look all these things up, but there's a LOT to learn. I'd have to know about mining, metal smelting, electrical engineering, electronics engineering, physics, chemistry ... the list goes on and on.
On top of that, you have to have leadership and management skills. Like you ask about "how to hire locals". Lots of people with a great idea or great technical skills have tried to start a business and gone bankrupt because they don't know anything about management. Motivating people and getting them to follow you is a skill in itself. This is not something that can be learned in a 10 minute session.
You ask "how to rule and form society". Yeah, good question. Just because you have technology that they don't doesn't mean that people will want to follow you. When Europeans went to Africa in the 1800s, they had lots of technology that the locals didn't. Did the locals immediately hail these Europeans as their new leaders and make them king? That was a popular theme in fiction -- European goes to Afghanistan tribesman, shows some modern (19th century) technology, and they immediately make him their king, if not their god. In real life, I'm not sure that that ever happened. The Europeans often used their superior technology to subdue the locals by force. But that took an army. One man with a machine gun might be able to subdue a few dozen people with swords, but not a nation. If he's obnoxious enough, sooner or later they'll overwhelm him by shear numbers and kill him. And with just one man ... you have to sleep sometime.
And would they be wise to make you their king? So you understand technologies that they don't. Does this mean that you know anything about how to run a country? What sort of tax structure should your government have? What economic policies? How do you negotiate trade deals with other nations? How do you lead an army?
You seem to be assuming that because your time traveler is from the future, he is not only an expert on technology, but also on politics, economics, management, finance, military affairs, and every other conceivable subject. Just being from the future wouldn't necessarily make him better at ... any of these things. And while he could study and prepare, no one is going to learn to be a great engineer AND a great politician AND a great business manager AND a great economist AND ... AND .. AND ... Certainly not with one year of study. Most people spend their lives studying just one field and never rise above mediocre.
I'd think a realistic goal would be to try to jump the people forward a century or so. The printing press was invented in 1439. So learn how to build one and then take this knowledge to 1300 or so. That would probably be doable. And be content to be an engineer, don't try to make yourself king and god at the same time.
By the way, I doubt the problem would be how to fight the church, but rather how to get the church on your side. In the Middle Ages, the church was the people who ran the schools and sponsored scientific research. Monasteries were centers of learning. Many great scientists were priests or monks, from Gregor Mendel to Copernicus. Yes, yes, the Catholic church persecuted Galileo. But Galileo started out with the support of the church. He had new ideas and of course people questioned him, but it was all a polite, scholarly debate until Galileo started insulting powerful people for not instantly accepting his theories. Anyway, a monk or priest would probably be the first person of the time to embrace new science and technology.
Update: Let's be more positive
So how could you realistically go about it?
How to prepare
Step one: Come up with a plan for what technology you can realistically introduce. Just bringing a truckload of 21st century gadgets to the past would be mostly useless. The people won't be able to reproduce them because they don't have the infrastructure. Many wouldn't work in any practical sense. A cell phone is useless without a network of cell phone towers. A sports car is useless without paved roads. Etc.
Figuring out what you could realistically bring back would be an exercise all on its own. I'd pick two or three key inventions. Most 21st century technology would probably be impractical; more likely bring back some 19th century or earlier technology. Introduce the printing press 100 years earlier than it was really invented. The steal plow revolutionized agriculture. Maybe something medical or chemical? Could you bring back electricity? If you could teach people in the middle ages to build electrical circuits, that would jump start all sorts of technology.
Of course you would have to thoroughly research whatever technology you are trying to bring back. There is, of course, a huge difference between being able to drive a car, being able to repair one, and being able to build one from scratch. If this is a one-way trip, you don't want to get there and suddenly find yourself saying, Oh, wait, there's one thing I forgot to read up on ...
Research the infrastructure available in the time and place you're going to. You don't want to get there and find out that, while you need, say, aluminum for this device, the people there have never heard of aluminum and have no idea how to produce it. Make sure that you can get everything you need. You may need to research not only how to build this machine, but how to find metal ores that you need, and mine them, and refine them. Or how to synthesize particular chemical compounds, etc.
I'd practice actually building the thing using only materials that will be available at the destination.
Learn the language of the place you're going.
That's a lot to do in a year. 'Hope you're industrious.
What sort of vehicle
Well, I'd rule out any vehicle that requires paved roads or runways. Possibly an all-terrain vehicle of some sort. I'd think a boat would be most practical. Sure, you're stuck on the rivers, but that's probably more versatile than being stuck on roads or open terrain.
Whatever vehicle you bring, consider how you're going to get fuel for it. Unless your plan includes teaching the people how to find petroleum reserves and build oil refineries, any modern engine will be limited to the fuel that you bring with you. I'd look into what sort of fuel people of the time use, Kerosene? Some unrefined oil? Maybe find or build an engine that runs on that. Or, maybe an electric motor and run on solar power. The solar panels will break or wear out eventually, and will almost surely be impossible to replace, but it could keep you going for a while.
Is there a limit on the size of the vehicle? If not, perhaps the bigger the better, because then you can bring back huge quantities of stuff, even if you can't move it once you get there. Someone on here mentioned a nuclear-powered aircraft carrier. Or a freight train.
What to bring?
Books fully describing whatever technology you're trying to bring back of course. I'd lean toward printed books despite the size and weight. Sure, a computer with a terabyte hard drive could hold way more information than you could fit in books in a big truck, but what do you do when the batteries die? Or the computer breaks? Will you have the means to repair it?
Presumably you need basic supplies to keep you alive until you can establish yourself: food, clothes, medicine. I'd bring at least some weapons so I could defend myself if things went bad. Tools you will need to build whatever technology you're trying to bring back. Especially, tools to make the tools you will need.
Make a good impression
Hmm, well of course step one is to learn the language, and learn the customs of the place. Don't go urinating on their sacred shrine and so forth.
Don't suppose that people will flock to you because you have scientific knowledge they don't. At first they won't even know if what you're saying is true. I mean, if you tell them, "I know how to build a machine that flies through the air" or whatever, why should they believe you unless and until you've demonstrated it? Just like if someone came along today and said that he knew how to build spaceships that can travel faster than light, would you just believe him? Probably not.
I suspect the best approach would be to start with modest claims, i.e. things that don't sound unbelievable and that you can actually do on the spot with things you have brought, or that you can build fairly quickly.
Do I even need to say: Don't tell them that they're all ignorant fools and you have come to bring the light of wisdom and knowledge to them, and they should all fall at your feet. Don't ridicule their culture, their government, their religion, etc.
Hire locals
I think that's pretty straightforward: have something to pay them with. Bring back some gold or silver to get started. Maybe you could bring back hand tools, pots and pans, or things of that sort that people would be willing to barter their services in exchange for. If you're bringing back a technology of value, you should be able to find a way to make a profitable business out of it, or to get the patronage of wealthy people. Oh, figuring that out should be part of the plan you make before you leave.
Deal with the church
Contrary to popular modern mythology, the church in the Middle Ages was a major -- probably THE major -- supporter of scientific research. Yes, Galileo clashed with the church. Can you think of another example? People did not go around saying that every new discovery was "of the devil". I am not aware of any case in real life of a scientist or inventor being accused of being a witch by church authorities. Many, many scientists of the time were priests or monks, or taught in universities that were run by the church. The church is more likely to be your friend than your enemy.
Of course if you go around saying the church is teaching a bunch of superstitious nonsense and that church leaders are all ignorant fools, you're going to get into trouble. Insulting powerful people in any place or time is not generally a strategy for success.
