Too many variable to give a specific answer. Once a week is probably
enough. I assume you made drainage holes. Don't want those babies to
rot. Letting them almost dry will encourge more root growth.

You might want to give them natural light during the day since you only
have a few. I don't know if the lights in your bath are strong enough
unless they are just inches above your plants.

I wouldn't fertilize right now. It might result in weak grow unless
you're getting strong sun light.