stocking ideas

I would keep the clowns but ditch the yellowtails, I would look into a school of Anthias or Wrasses, Maybe both. Also a mixture of tangs, naso blonde, powder blue...
You could have many sweet options.

Hey if you live near Philadelphia and ditch the yellow tails maybe i could have them? My 30 gal has 3 green chromis do you think they would be compatable. Also i would definitly keep the clowns.

The clowns should be fine, they stay fairly close to their homes and dont wander too far off in the tank. As long as the other fish are well fed I see no problem at all.

Darn Oh well ill just need to get one from the fish store.

I would actually stay away from Naso species. They get too large for even a 150g eventually. There are a good number of other tangs, like many Zebrasoma, Ctenochaetus species, blue tangs, etc. that are more suitable.

Personally, I would stay away from any more tangs in that size tank. I am sure a yellow will be super happy in a 150, but adding any more may be too much. If you do add another tang then I would go with Amphiprions advice, those would be the best options for your setup without question. I would focus on other types of fish instead of another tang.. angels, wrasses, blennies.. heck, even a Butterfly like you mentioned would be a better pick than a second tang IMO.

I wouldn't worry about your clowns.. they can hold their own against most other fish (and humans when they want to! My old Maroon clown used to bite me so hard it would draw blood).