You can feed 5-6 small fish. The important point is which species will it be?
If the number of fish and the number of corals increase, you may need a protein skimmer. I do not know which skimmer is suitable, it is connected to the sump chamber.
I have not used this aquarium before, but when I searched on the internet, I read that the return pump makes a sound. You have to use the return pump and look at the sound level. Probably no protein skimmer is included in the package (I may have read wrong).
I do not know the price (I do not know the American market), it is necessary to compare it with its counterparts.
Sorry for my bad English.