Alright, first of all we normally discourage the asking of multiple questions on a single post as this site works on a single question, single answer model. That said, the answer to all your questions is the same;
I could break them all down individually but in the end they are all just facets of the same problem, which is that you can't live in a virtual world completely and survive. You still need to eat. You still need shelter. You still need a job so that you contribute to a real economy because you're going to consume real resources out of that economy and you cannot help but do so.
Time is subjective to be sure; 'time flies when you're having fun' after all. But, time is a real resource in the real world, and the brain may well be capable of being stimulated really quickly, but that doesn't slow down time as the real brain perceives it. It just gives you more to do in the time you have on hand.
Economies are the same; your body needs real food and shelter. Living in a virtual world without nourishing your body means you'll eventually starve to death. In point of fact, dehydration will get you first, but the point is still valid; you need access to the real world to support your real body. Food. Shelter. Medicines. More. To access those you also need a real job. In other words, you're expected to contribute to the economy at least as much as you consume from it.
This leads to the question of war. If food or medicine or petrol or gold or uranium or whatever you need is scarce, you need it and your neighbour has it but won't give you any, war is inevitable. A virtual world doesn't change that fact for the same reasons mentioned above.
As for the science in the remaining two points, the important point to remember about a virtual world is that it can only model what we tell it to. More fundamentally, it can only model what we already know about. Science is about discovering what is unknown, or refining what is known to make it more precise or more accurate. Therefore, it is literally impossible to develop new science via a virtual environment because it can only model what is known, using the models we currently have. If a new scientific discovery turns those models on their heads, the virtual reality cannot model the new understanding without being reprogrammed to do so. If it isn't, then any effect we would observe in that virtual environment would not reflect the new understanding and would merely reinforce the thinking as laid down in the model it currently contains.
This is not dissimilar to questions that sometimes arise on games like World of Warcraft or EVE Online as to whether, with that many participants, they should create their own virtual country. If you can eat the food contained in EVE, use the medicines there, and only consume services that the game provides, then I say fill your boots.
For the rest of us who need to eat, wear clothes, live in houses, drive cars, and seek treatment from real doctors, we need to get busy contributing to the economy that will support those needs.
That's the one here in the real world.