I don’t typically agree with Nader, but 12 does sound fairly reasonable. It’s two consecutive Senate terms or six consecutive House terms, which are plenty.

I’d make an exception with the supreme court, where a term is 18 years instead. With 9 justices, that comes out to a new justice every 2 years if you spread it out equally. They’d also have a strict term limit of 1 term, you can’t serve as a justice more than once.