If you want to play games that focus more towards realism, then stay away from high caps as they are not permitted at those games.
BB weight, you will find what works best for you, but don't go lighter than 0.20 grams. The heavier you go the more stable they tend to be and you gain better brush penetration but you can sacrifice some range depending on your gun.
If you are going to be out in the forest or desert I highly suggest getting a camelbak for water (3 Liter at minimum) and a load bearing vest of some kind to keep your mags and extra gear in.