Do I Need to Sand My Paint Before Applying Polyurethane?

In my experience, you should always sand after every coat no matter what materials you're using. It helps achieve a smoother finish overall. But ultimately, it's up to your desired outcome. Sounds like you're on the right track by considering your options!

If you're aiming for a smooth finish, it's usually recommended to do a light sanding between coats. But if you decide to put poly over the paint, definitely don’t sand the last coat—as that could just remove the paint instead! Using a good paint that offers a solid finish might save you the hassle of the poly altogether.

You might not really need poly over paint since paint itself is a decent protective layer. Are you looking for a clear coat finish? If that's the case, more layers of paint could do the trick without needing poly.