I have a heat pump, and central air, split system. I bought this house a couple of years, which was built in '87. The air handler is a Trane, the outside unit is American Standard. I'm assuming maybe the outside unit was replaced at some point, being a different brand.

The maintenance I did:
I cleaned the electronic air cleaner, and prefilters Replaced the wall return grill air filter
Vacuumed out dirt in ductwork behind the wall filter housing
Vacuumed out dirt from the ductwork under the EAC
Vacuumed off the coil prior to the blow assy.
Checked the outside unit to make sure it was clean and unclogged from debris.

Anything else I should do or look for?

How often should I have it inspected by a qualified technician?