[Hectic]

Yup 450 is fine and "upgrades add more" is a false statement the only uograde that will add significant fps is a spring.
Yes some other uogrades wilo net you 5 or 10 fps but the fps isnt the reason for upgrading. You change things like the spring guide and trigger sears and piston for durability.
You change things like the inner barrel hop up cylender head to increae shot to shot consistancey (the single most important thing in airsoft sniping).
As for the certification. Most of the oldschool guys who host will accept the certification and allow you to use your lvl2 or lvl3 certification limits 500 and 550 but there are other factors. As a new player they may not let you use above 450 even with certification. The field may not have space for safe mi.imum engagement distances so above 450 is out the window again.
If you wanna play as a sniper the first thing you need is a good sidearm. After that get a good base gun to upgrade (vsr10 l96 or aps2) stay away from gas stick with spring.
After getting the gun get a spring 400-450fps get a bearing spring guide get a hop up unit a good hop up rubber and a good inner barrel and stick all that stuff in to the rifle. Get a good scope to stick on the gun and build or buy a ghillie suit to stick on yourself and a wrap for your gun.
Last and probably should be first is buy some good bb's either 0.36 or 0.40 then sight in your rifle at a medium range say 150feet or so.
Then practice see where you have to aim on your good mildot or range estimating scope at all your ranges. Obviously at 150 feet it will be dead center and from there youll have to adjust for closer and further ranges.
Closer then 75 feet you should engage with your sidearm (but really you should never have to do this unless you messed up and blew your position and the enemy is closing in on you)
Once you know how to shoot you should learn how to move undetected and how to hide in plain site. Most of the learning is better done with an aeg then when you fuck up( and you will) youll be able to fight. Once your good at movement and concealment then your rdy to grab your bolt action and spend all day layin around in the mud looking for that one good kill.. Maybe if you even get one at each game.
I think that covers the baisics. Good luck welcom to airsoft.