When working with exterior boards, it's crucial to prime them with oil-based primer before installing. This will seal your wood and prevent water damage. We used Zinsser which can be found at most home improvement stores. Oil-base can be tricky to work with, so the key is to use long fluid strokes and work quickly. It dries super fast, so keep calm and roll on.
If you need to pause inbetween paint jobs, no problem. Just keep some plastic bags on hand. Wrap your roller and tray each in their own bag to avoid from drying out. Then you are good to take a quick break!