Not huge on the "mil-sim" guns. play hard and you'll do fine. I would recommend doing your own LP on it.
Polish surfaces and striker (if you have the old solid striker trade it to the newer or get a light one)
tech-t has a-5 valve springs (only that i've ever seen).
Reg screws into the ASA, at best i'd expect 400psi anyway.
Pick up a different barrel, stock barrels are know to have loose tolerances.
Bolt and power tube are best if stock. Only upgrade if they break.
Cyclone soft paddles. The headaches this will save you.
If you want faster, e-grip and upgrade your cyclone. Ratchet and QEV.
The response trigger is kinda nice because its simple like the gun. It turns the gas hog into more of a hog =P but depending on where you play check your rules first.
experimental valve if you get get bored. I played with it in stock configuration and tested out a reg, but results from one of the fastest bt-4's you can find use this design. Basic Idea is the same as spyder, increase volume and direct flow. Dremel the tiny square channels with the large drum and then polish it. electric tap on the portion that doesn't so it air only flows over the channels when in the power tube. I can only confirm that my kick and noise reduce quite a bit, the FPS dropped but since the stock spring is so goddamn heavy its in a normal range. Efficiency is unknown, but not terrible either. If I did it again, I would have done the smaller drum first just for testing, then move up. I might continue further at this point but who knows.