I have run my Husky for over 2200 hours. I never did anything special
at 500 hours. I did proactively get new magnetos at 2000 hours. I
wouldn't change the vacuum pump till it fails as you dont fly IFR.
Other than that, just wait till annual and do the normal stuff that
needs doing. All Ive done is replace the broken parts and have not had
any major trouble.

Inspect your throttle cable, replace if necessary. If that breaks, you
are hosed. I dunno, dont they check all this stuff at annual? I've
never heard of a "500 hour" on a small GA aircraft.

Does Piper call for it?