Welcome Beany. A nice small tank like that can easily hold 4 zebra danios. If you have a good feel for how much food to use, they can be fed daily. The problem many new fish keepers have is judging how little food is needed for daily feeding. In that case, every other day is often enough for the fish to survive and too little food is much better than too much. If you can get a feel for how darned little the fish need for food, they would benefit slightly from more frequent feeding but remember the issue of not overfeeding.
As far as the filter cleaning, I only clean my filters when the water flow slows a little. Until then, I figure an undisturbed filter is better than one that has had too much cleaning done. your filter has a very high flow rate for a tank your size but there are those here who would advise that much so it is probably OK. You should not need any carbon but it won't hurt to have it present. If you get into a situation that demands carbon, you should be aware that it is only active for a short time after you start using it. After just a week or two, it will be totally ineffective as a chemical filter but won't hurt anything to be present in the filter.
How long did you work to get the filter ready for your fish? By the sounds of it you are using the zebra danios for that purpose. If so, please read the thread about fish-in cycling. There is a link to it in my signature area.
