Welcome to your next obsession and black hole for money!
I personally think that UV staerilizers are more detrimental than beneficial in a reef; in a fish-only, they are really useful!
Angels are a good addition for a tank that size; one of the smaller "large" angels would be really cool. I would get an anemone for the clownfish to hide in if the angel got too rowdy; though with that space, and if you got one of the more docile, smaller, "large" angels, it probably wouldnt be a problem. What kind of lights do you have as of now? That issue will be an area of much grief in the future if you dont address it now, and decide exactly what (or what type, really) you want to keep in your tank. If you just have flourescents, buckle up for a fairly major lighting change and budget bash...
I would also keep maybe some of the smaller butterfly fish, and perhaps a small group of them; theyre really the only peaceful fish thats large that you will get that awesome schooling behavior out of. A group of 3 or 4 would make a spectacular show, as long as theyre pretty small butterflies!
Hope that helps at least a bit!