I would say that 7 fish in a 55 is too many. The clowns, depending on the species, will get to be about 3"+. Thats 18" of clownfish. If you stick to a 5 gallon/1" of fish rule...a 55 gives you about 11" of fish to work with. You could probably put in more then 11" of fish considering your aiming for a FO tank. Also, when considering clowns, many of them can only be kept singuly or in mated pairs. Perculas and tomatoes are exceptions i think. Maroons are definately out of the question. Also, that regal tang is probably a bad idea to put in the 55 by itself, let alone with a bunch of clowns. They are teritorial, and will get very big (9+ inches.) I would say, start out with a mated pair of clowns, and then move on to a smaller type of tang if you want one. Also, if you have a 55 regular (48" in lengh) this would be much better for a tang (they like swimming space.) As for clown/tang interaction. I have a maroon and a yellow tang in a 75 gal and they get along fine.