I totally back using a 300-350fps gun for beginners. You can use it inside and out, and FPS really doesn't make a big difference in range and accuracy. It does however make a big difference in safety
I've owned, used, and seen many <360fps AEG's outrange 470fps sniper rifles.
Proper compression, high quality hop rubber matched to FPS range, proper BB weight for FPS.
Infact, I've made a stock tokyo marui P90 shoots accurately out to 200 feet at it's stock 300fps
All I did was regrease the mechbox, ensure proper compression, and the only upgrade I put in was a clear guarder hop rubber.
That being said, you don't know what you're rifle does until you field it. And you have to really KNOW what it does. Don't just take it to one game and throw $400 of upgrades into it. Do research and ask around, figure out what you need to upgrade first.
The best upgrade you can do to ANY gun is a simple $15 hop rubber, and it's one of the most important upgrades.