I’d just keep it to similar offices - 16 years as any kind of state or federal judicial office (okay to have 16 years in each), 16 years in Congress (both houses) or the legislature (both houses again), but 16 in the state legislature and another 16 in Congress okay, etc.
The only appointive office I’d hit with term limits would be judicial. Federal judges are incredibly arrogant and, as Supreme Court justices, can do incredible damage. So term limits for judges is pretty much damage control.
I could care less if some bureaucrat has a career - most of them are working stiffs like us, and expertise is pretty important for many. You can risk your kids’ lives on some water quality guy with only eight years experience - I’d rather have my water quality guy have twenty years experience.
I recall a situation 20-30 years ago when a Post Master over the area I lived in at that time did something that infuriated the local community. Complaints did not go to the Post Office General, but to our local Congressman. It was he that nominated the local Post Master to the President, and it was the Congressman that stood to lose if he did not move to correct the situation.
What we had then was greater local control.