Another good fish to start with is the royal gramma.. shy but very beautiful. if you are after clowns then try to get 2 smallish ones of the same size, then you are guarenteed a pair as one will chnge sex to female as it gets older. Clowns dont do so well on their own as they prefer the friendship of a partner. Dont make the mistake of thinking a clonw "Needs" an anemone abecause they dont and I strongly advise against purchasing one also. If you want them to host then use a Sarcophyton leather mushroom, less demanding, far easier to keep, doesnt kill fish and clowns will host in them.
As for the size of tank... get the largest you can offord to keep. this makes the whole job much easier because water perameters will remain stable far easier. If you are considering tangs as a future purchase then be warned, they need a minimum of 100 gallons to live in.
Hope this helps.