Get one first...play with it. Then figure out if you need to upgrade/tweak anything at all. LOTS of guys start out with 280-320fps rifles....indoor and outdoor.
There's less risk that you're rifle will fail, it'll work better/smoother, batteries will last longer, you can run indoors and outdoors without changing anything, etc....lots of upsides to lower FPS.
You'll spend more time playing than spending time/money on upgrading your rifle...and then more time/money "fixing" your upgrade.
Playing with a reliable rifle is A LOT more fun than being down and out because your rifle self destructed during a game (or the evening before a game).