well, the hippo will be too big for a 75, the really need a 6 ft tank. you could go with a smaller tang like a scopas, or kole maybe.
How do your 3 clowns get along, usually they are only kept in a pair and they drive off the third.
the mandrin should be added after your tank is well established and hopfully you will have a fuge for pod production.
The diamond and the sixline will be fine, but not sure if multi dwarf angels will get along - maybe only one.
with those fish, you will be pretty full, maybe something small like pair of banggi or pj cardinals.