Welcome to R2R!
To me, this looks like a 2-part question:
1: Food to cycle a tank
2: What to feed clownfish
For cycling, the standard way of cycling a tank is to add enough of a nitrogen source to get an ammonia level somewhere in the 1-2 parts per million range. Do that once, then wait until ammonia reaches zero. Then you are ready for your clowns. The nitrogen source can be fish food, pure ammonia, or a few other options. The ammonia source really doesn't matter much, in terms of the tank cycling and being eventually safe for fish.
For feeding the clowns, variety is best. I feed my fishes a rotation of frozen Mysis, frozen spirulina brine, and flakes. Nori sometimes for the tangs and rabbit.