First of all Welcome to the Forum!
Technically there are no upgrades that you "need" to get. As for what can you do, that all depends on how mild or wild you want to go. You can get a regulator, although I'm pretty sure this requires you to change out the VA (vertical adapter). Spring kits, valves, bolts, strikers and barrels, pretty much cover everything you can up grade. Me personally, since I'm a tinkerer, I would do it all, but at the minimum, I would recommend a regulator, which mean upgrading the VA as well and a spring kit.