The bolt should be relatively simple, just get a bit of locktite on the screw and then place it in. I've done that for all my sniper rifles. As far as upgrades go, I'd stick with a tightbore barrel, a bucking, and the PDI upgrade kit [spring, spring guide and piston]. That's inexpensive, but you'll notice a immediate increase in performance. Army Navy has all those parts, I believe.
Another thing, and this is important: PLEASE be careful with your trigger box. Those mechanisms will work fine if you take care of them. If your gun jams, don't keep pushing the bolt in. Pull it out, drop the mag, and clear out the jam. New trigger boxes are hard to come by, but taking care of it will last you plenty long
