Pat welcome aboard.
Engine oil, gear lube, anodes, and gas filter should be changed yearly. Most of us do this as part of the winterization process as it allows one to identify any potential issues and have time to address them before next season.
Also old oil has acid that eats at bearings.
Impeller every two years.
Depending on the bottom paint every year or two years.
Check bellows for cracks.
Check exhaust temp with a handheld IR sensor. These are water cooled and need to be replaced every five to ten years if in salt water.
1997 2400 SCR
5.7 Vortec / Bravo 2