As mentioned multiple times before, start out simple.
Standard rifle buffer, standard rifle spring, put a hundred rounds through it to make sure it works.
Then, add enough quarters to take up the bolt overtravel, I think I had $2.75 in mine, then I made a delrin spacer to equal that thickness to replace the quarters.
I built my rifle for competition in 2012, 16" YHM barrel, DDLES (pre QC-10) Colt mag lower and bolt, Pro-Mag poly mags, yes, Pro-Mag. Got tired of dropping my $30 mags in the dirt, bought an $11 Pro-Mag, took it apart and deburred it until follower was completely free. Worked flawlessly, bought a whole bunch more of them. Had a GI trigger at first, put in a Rise Armament drop-in when they came out.
Probably 20K rounds, many wins, and the only issues I've had were operator induced. You can over insert a Pro-Mag poly with bolt open, screws up your stage times.
I've seen lots of guys with lots of different combinations of buffers, springs, spacers, bolts, etc, have lots of problems, don't over complicate things.