most grows that ive read about, use from 3-5 gallons, 5 reportedly being better. and there isnt any reason to veg for 3 months unless you are trying to get huge plants. 2 months should be fine. though i did mine in 2 gallon pots but it was only a 14 wk grow and they did get rootbound. plus your room is a lot better than mine ever was, so i would expect some really nice plants from yours.