I usually feed mine every three to four days, and let them eat all that they will. I've found that when I feed them every other day, my younger taricha pretends to be finicky and I have a hard time getting her to eat. It's up to you though, if they seem to be doing good with what you've got going on, then I think that is fine.
I don't know if it applies to all animals, but I know that with some fish (particularly bettas) it's good to let them go without food at least one day of the weak so that their system can clear itsself all the way out. Maybe this applies to newts as well? Anyone else have any ideas on if this is true? If so, you could let them go the weekends without food or something like that. Just an idea.