Most cabinet interiors are melamine these days. That's a great surface for shedding water, and keeping clean. It's not so great a surface to try to paint. It's a lot of work to prepare properly, and even then, a painted interior will need shelf liner to keep your stored items from "grabbing" the paint or chipping it.

In short, I'd not paint the interior. Just empty everything out and clean it up well. Maybe put in new shelf liners to make it "new".

We *just* painted ours last week. And we did all front surfaces, and the backsides of the doors, too. We did not paint the insides of the cabinets at all. I think it looks great, was fairly simple, and the insides would have been much more work for little benefit.

We did not paint the insides of the lower cabinets.

We just painted all our insides, before we start on the outsides. It was varnished plywood, now is gloss white (with squishy plastic shelf liners on the most-used shelves).

It really makes a difference in how the cabinets look when the doors are open, and how easy it is to see things in the back recesses.