Not to jump on the band wagon with the whole TANG issue, but from my experience, I had a 7-9 inch Blonde Naso in a 180 which is somewhat larger than a 125, only in height, and he did well for some time and then out grew the tank. I originally got him when he was about 6 inches and then I had to take him to the LFS for a larger tank. Just not enough swimming space when they get larger. Another point to think about with tangs is that they are fast swimmers, the larger they get, the more they might knock over a coral or two when you start your reef. Just my $.02.
As far as your fish list,
Look into either a flame or flameback angel or coral beauty.
I would go with the hippo tang rather than the naso for reasons stated above, that and I believe the hippo doesn't get as large, someone correct me if I'm wrong.
The clowns you chose are good, make sure to put them in first so they can find a home, a nice anenome would be good too. Although my clowns like my toadstool leather.
I would suggest the pink square anthia (see if you can find a male and female pair)
I would shy away from butterflies. There aren't too many that are reef safe and I know that they are prone to sickness in the aquarium.
Have you thought about a mandarin or citron goby or royal gramma?? Just some ideas.
Please take my advice for the naso as just that, advice. I don't want to get into this fued that the others are having. Remember this is a hobby!! We are supposed to have fun!!:cheer: :cheer: