Looking good! Depending on what other additions you have planned, you should be able to add a zebrasoma with no problem. Or a smaller type acanthurus. A fish that acts a lot like a tang is the foxface. You could have a regular one, a one-spot, or even a magnificent in your tank.
75 gallon, all HOB, and my 3 tang gang are getting along splendidly. Yes down the road there will be tough calls to be made but, for now they are the stars of the tank. Also, the blue is an ich drama queen; fluconazole and copper power spa for 2 weeks, back in the tank, then 1 or 2 days of angry a ichy. She's happy now... for now.