Install internal door frame in existing entrance and a dutch door

Hi, my suggestion for you is to take a measurement of the gap and get interior door and frame from wickes, it doesn't need to be exact size its better if new door frame slightly smaller so you can fit it easly and boarding will close the gap once all done and oil base paint will dry in 16 hrs but may cover in first or water base will dry with 2-4 hrs but may need 3 coat to cover. I hope this helps