If you buy a gun that shoots 500fps, with .20, it wont be allowed at any game I know of and is pushing the limits of legality (federal laws). Guns are tested at games with (normally) .20 ammo.
Use a standard velocity gun for now, and learn to use it well instead of pushing the safety rules. Most snipers I've seen shoot around 350fps anyway, and that is just fine.
When you learn to make that plastic BB fly straight and true by using your hopup correctly without you being seen, you win. Until then, there is no upgrade that will make any difference except as a risk to others.
That's the only trick; dont be seen. For the rest, get in contact with local players, go to games, see what's used and why it's used. There are a few excellent snipers in Quebec. (You may want to clarify where you live, it's a big province).