Is there a certain amount of hours that it is recommended to change both plugs and coils? Or jus run em till they quit?

Plugs you can change as much as you want, I do mine at the beginning of each duck season.
The coils are kinda a different thing, most run them till they develop a problem. Personally, I like to change my entire wiring harness (including coils) every 3 to 4 years to combat future problems. It's too cheap to even mess around with in my opinion.

With the newer style potted coils I would just run them till there is a problem, have seen the older open style coils work well for >500hrs in freshwater but for you guys near the coast I imagine its a whole different deal.