This guide is based on my own research and experience painting my own kitchen units and, more recently, the laminate units in my workshop. You definitely learn as you go!
A quick-drying,Non-shrinking filler will be adequate for this. Slightly overfill any holes, and when completely dry, sand smooth and level for your base product.
Tape up your walls and/or tiles with the masking tape where they meet the carcass of your kitchen and along the floor if you are unable to remove your kick boards.