Ok. Pair of clowns - perfect,
Yellow tang - not bad,
Hippo tang - your tank is way too little. They need 100+ tanks. 6 ft long are good options. Plus, they are ick prone. If you want to save yourself headaches, avoid the hippo until you are more experienced. I would also suggest a quarantine tank, and anything that is added to the tank should be quarantined for a minimum of 1 full month... ( 1 week for most corals) It sucks! I know. But it is a LOT better than seeing your fish get covered in ick and seeing them die.
Not to mention that if you do happen to get it into the system you will have to go a minimum of 8 - 10 weeks without ANY additions to the tank, including corals! If you are a patient guy it shouldn't be too bad. If you are like me, you are screwed...