Tim B is basically that it wouldn't differ too much from any other society with sufficient technology. Where I don't agree with him is that the equivalent technology would be significantly better than those our ancestors had in Middle Ages, so it would be a lot different.
I still have a vague idea how the element control would be potent, so I'll guess. Correct me if I get totally out of your ideas.
Mining and building
For mining, I guess the effect would be roughly equivalent to modern machinery, just cheaper, if the work is undertaken by those with particular talent. With medieval technology, it was possible to dig 10-40 meters of a tunnel per year (depends on the hardness of the rock; it digging through soil, it would be much faster, even kilometers per year). Good earth controllers would be able to dig several meters a day - completely different pace, making mining much cheaper.
Underground cities like Moria were not possible in real history, unless there already was a cave system requiring only minor changes. Underground building would still be more expensive than ordinary building on the surface, but not so much. Also, with so many people digging underground, earthquakes would be much more common, so at least in mining areas, the houses would somewhat resemble Japanese architecture in their resistance to earthquake.
Fire and metal controllers would make industrial revolution possible even without blast furnaces. Metals would be cheap and used a lot. Steam engine would be easier to discover, but its invention is not automatic, so this doesn't have to become a classical steampunk. Industry can also rely heavily on water experts moving water to high ponds, from which it would flow and be used for mills and similar machines.
With air and water experts, weather wouldn't be quite easy to control. This would make good crops almost granted for those who can manipulate it well - and hurricanes and droughts frequent where the controllers are absent, inept or disorganized.
Water transport would be much faster - manipulating wind and water flows locally would be easy. Land travel would be as slow and expensive as in real history, so all goods will be moved by ships if possible.
Like steam engine, balloons or kites would be quite easy to invent, but not guaranteed; or perhaps some clever individuals would use kites or even balloons, but this technology wouldn't be commonly known. Anyway, air travel seems quite possible.
All soldiers could wear heavy plate mail (see "industry"); the only reason against this would be that they don't protect well enough against fire and are prone to metal manipulation. So another good armor is made of organic material: wood, leather and bones, or even wet algae for those not expecting the enemy to control water, or controlling water themselves. Or light plates under leather coats, if the metal controller needs to see the armor to make it strangle its wearer.
Most widely used weapon would be plain element manipulation. Otherwise, soldiers would use bows, wooden clubs, swords or weapons somehow associated with their element - like bags of ice or coal "grenades". Anyway, ranged combat would dominate over melee.
Gunpowder seems unlikely to be invented early, because fire controllers would easily outperform it. But experts on other elements want to use such powers as well, so there would be a need for it if someone provides the technology.
Mining would change the fortification: making a fortress underground would be possible, and much more resistant to air strikes by air controlling enemies or siege mining by enemy earth-controllers. Better underground fortresses would have layers of something hard to control around them, playing the same role as walls had in medieval castles - to prevent the enemy from moving in. I don't know what should it be, but there should be something solid and hard that nobody can control. It could be quite expensive (such as amber and corals). Wood would be a cheap solution, though once exposed to air, it could be burnt by fire controllers.
Underground warfare would be much less like classical fantasy man-to-man combat. It would focus on digging, producing earth-ins, striking enemy diggers with flames, trying to open paths for water to drown the enemy and trying to cut the enemy out of sources of fresh air. Ventilation shafts would be the weakest spot of any underground fortress, so they would be hidden or fortified to prevent the enemy block all ventilation shaft and let the defenders suffocate.
If flying is possible or even common, the surface fortifications would be something between classical castle and modern bunker: the roofs would be hard and with no big gaps. Otherwise there can be classical castles. Anyway, the walls would be usually wider (making a hole through a thin wall would be easy) and preferably made of materials hard to control, such as wood, leather, bones etc. The biggest castles would have several lines of defense made from different materials, so that the enemy would need several teams of different experts.
Anyway, with fortifications so cheap, the most wars would consist of several long sieges, fighting in the field could be seen as somewhat unorthodox tactics.