No problems at all, an 850w is more than enough even for two 570's. Since you have an mATX board, you won't be able to add a second in the future, so you may want to look into getting the fastest single card you can now if you don't plan on upgrading in the foreseeable future.
Probably no big problem.
I had a GTX580 in a v351. Loved the case in red.
When I say probably, you need to avoid the GTX570 cards that have coolers that are higher than the rear panel slots. Some have heat pipes that will not let you slide in the motherboard with the graphics card already installed. Get a GTX570 with the reference direct exhaust cooler. I had no problems with cooling the EVGA GTX580. If there is a cooling problem, it is with the cpu coolers which must be limited in size. The case does not have sufficient exit air area for the cpu.