You'll want to upgrade the screws in the bolt carrier, as the ones in it have a tendency to strip the heads or back out during firing, jamming up the gun.
Also, your perogative, but many like to replace the two piece screws that hold the gun together with HK pushpins, which are tool less design.
The barrel can unscrew from the trunnion, so apply some thread locker to the large screw under the back of the forward handguard to make sure it doesn't back out and leave the barrel loose.
The gun likes CCI Mini mags and Federal bulk pack the best.
I miss mine, wish I had it back. Had done the above upgrades, and replaced the furniture with actual HK variants. Much more solid and reliable.