Original countertop was a formica type product. If you want to preserve it, I would not use a belt sander - it has the potential to chew right through the formica…
Instead use a safe stripper type product. I have used SmartStrip by Dumond - available at Sherwin Williams and some Home Depots - very safe on the user, the environment, and on most plastics. Try it on a small area first to see how quickly it works and that the formica is not affected. Some paints lift very quickly and are easily removed with a plastic scraper. Other paints may require a longer time to lift and you may also need to cover the stripper with plastic to keep it moist for the longer wait times. Make sure you protect those areas where you don't want the stripper!
Let us know how it all turns out - photos are always appreciated...Geo