DMR Buidling - Help Needed

OK guys.. I just bought an DMR for like 250euros ~ 350 $ . I bought it from my friend which did some upgrades. But Off course thats not all so I am asking you all know.. Here is the "Config"

A&K SR - 25 Full Metal
5KU Air Seal Nozzle for SR-25 series AEG
SR25 Extensive Tappet Plate
Element Hop Up Cushion for AEG
Lonex Hop Up Rubber (70 degrees)
Modify Spring - S150+
Battery 9.6 V ; 4200 mAh ; Dean Conectors
I have optic so thats not needed.

All othes is STOCK !

So it has about 450~500 FPS


Now I am wondering what else should I upgrade ? Or what to change ? And off course I am interesting in current condition,with BB-s . Shall I use 0.36g or 0.43g for this configuration. Off course when I choose to upgrade more I will use 0.43 g for best performance.

In my country its allowed ~505fps and only semi -auto. So take care of that when you put some tips or anything else.
Please give me some advice because I am new in sniper world

And off course,from DMR I want RANGE as primary role . If you know what I mean Thx !