Trimming .308 cases to 1.9685" (50mm) won't hurt anything, but it'll be a reason to clean the chamber mouths very good. I've kept mine from 2.000" to 2.010" and trimmed 'em when at the upper limit back to the minimum.
I've seen all sorts of "standards" for bullet seating depths from some fraction of every round's dimensions possible. In reality, as long as the bullet's held secure enough for environmental handling and loading, pick the depth you smile the most with. One of my .308 Win. match barrels started out with 190's being seated about 1/4th inch into the case and would shoot about 1/2 MOA at 600. I kept track of having to seat them until the throat had eroded enough so bullets' bodies were only held by about 1/100th inch of the case neck and would still shoot 1 MOA at 600 yards.
Most bullets shoot most accurate when they're touching the lands when fired; Berger's VLD ones seem to do best several thousandths off the lands.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master