You're supposed to be able to use chalk paint without having to sand first. If that's not a look you want, you'll need to sand the stain and sealer off then wipe all the sanding dust off. Also, mark doors and hardware so you know which ones go with which - and where they go back when you're done.
A good quality paint can also have primer already in it. Remove hardware first, and keep a wet rag handy to quickly wipe away any mistakes.