There was a time when running a PCC was a pain in the butt. Bolts were cut for either glock mags OR colt mags, but not both. These days, most bolts will accommodate both.
The bolt profile also had an effect on trigger compatibility. What I found the safest route was to stick with milspecish trigger groups. Meaning triggers that use a full power hammer spring. I always stuck with either geissele or some form of schmid. I never had a problem with either.
As for the rest of the build, stick with standard buffer springs. The only reason to go with a heavier spring is if you need it to help with recoil recovery. The spring weight has little to do with the actual closed bolt lock time, for lack of a better term.
When it comes to buffers, avoid solid buffers. You want to use a buffer with sliding weights. This will help with bolt bounce.
A good way to setup a 9mm pcc is to use a vltor A5SH buffer in a standard carbine length buffer tube and grab yourself a few tungsten buffer weights. This will give you a lot of flexibility in tuning.
I do have friends that run hydraulic buffers and they swear that it makes the rig run more smoothly. To me it just feels like the rig is sluggish. I like my rigs to run snappy.
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