Brass bushing and the TNA adjustable gas kit are vital.
If your gen 1 is early enough that the gas block is pinned you won't have nearly as much risk of piston breakage as the later unpinned POSs.
If your gas block isn't pinned, try to find a smith than can pin it. If you can't, make sure the barrel is dimpled so that the gas block can't walk, use high temperature loctite on the grub screw, and buy spare pistons and springs just in case.
Aftermarket triggers are very nice, but doing the paracord trigger job trick can make the crappy mil-spec trigger much, much better. And it's free.
If you want to maximize longevity, swap to a gen 2 upper or go with the Spectre or TNA upper (and upgrade to a brass bushing if they don't already have one). They're properly anodized so wear is reduced, some come with shell deflectors. The TNA steel upper comes with a replacement bold carrier, where the carrier has a properly-fitted magnetic bolt handle that should never wear out or break.
