“Ghost feeding” is when you add fish food to a tank that has no fish in it. The fish food decays providing a source of ammonia for your bacteria.
Cycling a tank with Clownfish would a “fish-in” method of cycling, where fish metabolic waste, poop and uneaten food all add to the ammonia in the tank. It’s seemingly the least popular way to cycle a tank here on R2R as many would say that it’s cruel to the Clownfish, but this was a very popular method years ago and technically does work.
Another way would be a “fishless” cycle without with any live fish. You can either ghost feed or dose ammonium chloride.
Here’s an article from Dr. Tim’s Aquatics on fishless cycling. His ‘One and Only’ product is arguably the same as the Fritz TurboStart that you used, you would just need some source of ammonia for the bacteria:
https://www.drtimsaquatics.com/resources/fishless-cycling/
As for food, Clowns will eat almost anything from pellets to frozen, they are not hard to feed. Others may have a more specific recommendation though.
EDIT: And don’t use the “shrimp” method, it literally stinks!