I'd say get a Well MB01, it's the same gun, but the orange tip is screwed onto threads within the barrel while the UTG has an orange tip on the outside of the barrel that you'll probably have to pry off with pliers.
I'd recommend getting a 6.03 barrel because it's not too tight, but the bore isn't too big and it's been proven to be the best for snipers. Don't worry about the barrel length, I have a 650mm on my L96 and it's fine. If you want a 509mm for a great deal buy it here, it's where I got mine (A madbull ver II for $29.95, what a steal!)
Or you could get a PSG barrel which is 590mm for the same price:
As for a spring get a M170 sniper spring, that will preform the best without a chance of ruining internals and if you get the right upgrades, you could boost your snipers fps from 530-550, depending on how well your gun is upgraded. A M190 will go over 550 fps limits and a 210...just don't. Recently I had my gun chronoed at 490 consistently and all I had at the time was a metal trigger box, a M170 spring, and an aluminum spring guide and piston. If your L96 has more than that, you should be able to hit 530-550 easily.
I've also heard that a hard bucking is good for a PDI hop-up.
For an L96, a silencer that is from 8-9 inches is pretty good. It's all personal preference. I prefer a 9 inch (I made it) but I also need it to cover my 650mm barrel
You may also want to buy some better spacers for your barrel, it improves accuracy if you use a longer barrel.
I hope this helps and btw, if you're getting rid of or have no need of any of the old internals that you replace, I'll be happy to take them off your hands =D