How do I clean my aquarium without upsetting my fish? And how many fish should I be keeping?

In a previous tank I had I cleaned the tank and left the fish in there while I was siphoning the gravel and pouring new water in. They always seemed a little upset. Do I take them out and put them in a separate place? I am currently cycling a 75 gallon tank again for one fancy goldfish and two Ryukin. Is this to many fish? I know that they get up to 6 inches. Should I just keep one fancy goldfish and one Ryukin? I would like to have at least one fancy and one Ryukin. Any answers would be appreciated :)