I guess I should appologize for the tone of my post as I did nothing to help your problem or answer your question. To be honest I never considered that this was a temporary home and by temporary I mean like a month or so. I guess it is very easy to get frustrated when there is so much information out there available and some people just choose not to read it. Note I am not saying that this is the case in your situation, but it does happen.
To answer your question, PLEASE don't add any more fish now that you have a Tang in there. Ideally if you could trade him in where you bought him and get something that won't grow too large you will find your tank MUCH easier to maintain. Honestly I know I am pushing the limit with two Percula Clowns in a 20Long. I do have a 55 in storage which will be getting setup in a few weeks, so I know that as a temporary home, these fish are okay for now. If you really have a bug for clownfish, and can return the tang, you could probably get away with any Juvy as long as you don't add two. I'm not saying you couldn't pull off two juvys, but if this is to be a perminent home and you realistically aren't going to upgrade anytime soon I would really just stick to one, and try to stick to a clown that doesn't get quite as big as the others....ie no maroons.