Maroon Clowns are usually considered aggressive. They are also the most territorial of the Clowns. Cool fish, just tend to get aggressive as they get older.
The Hippo can get up to a foot long. If you've ever seen a mature one, you'll understand why they need big tanks. Plus, Tangs in general, need a lot of space to swim. Most suggest a six foot long tank so that they can get up to cruising speed. People have Tangs in "too small" tanks all the time and will argue that their Tang is somehow special because it "looks so happy and healthy". If you look at the Sick Fish section, you will see that just about every "my fish has Ich" post involves a Tang in an aquarium that is smaller than suggested. You almost never see that story with a Tang in an aquarium that is the proper size. That tells ya something (or it should). It could take a while to get larger. I tend to believe that keeping them in small tanks will stunt their growth. There are arguments to the contrary, but at the very least, it tends to cause health problems. I also wonder, if there is no stunted growth, why the people that have had Tangs in small tanks for years don't have full sized fish.