I think two more for an even 10 should be ok. Just keep in mind how small your fish might appear to be now, they will get bigger with proper care. Each needs their own swim space.
I got 7 fish in my 55 and I think I am stocked to the limit. I have two big fish (Tangs), and the rest are smaller fish. Yet they will all get bigger, so I am going to upgrade soon to a 180 gallon for my two Tangs.
Maybe a Six Line Wrasse and a Flame Angle will do well in there. Fish are all subjective and each fish is different. My two tangs shouldn't live together I was told. A yellow tang and a yellow eye tang, but they are schooling together and swim together. In fact all my fish seem to like to school together, especially around feeding time. LOL
The Yellow tang was damaged (Fins were nipped off) when I bought him. I got him out of a bad tank environment from the store, because he was getting picked on. All his fins are now grown back, and he is a awesome looking fish!
Another fish I can suggest because it only requires a 75 gallon tank, being you got an 80. Is a Yellow Eye Tang! It's an awesome fish, and mine is happy in his new home. For now. He is small enough to have plenty of space without issue. I know in a years time I need to go bigger, but my wife and I already want too and are saving for it. You on the other hand already got the size for a few species of tangs. I would maybe suggest a Tang off this list from Live Aquaria
Surgeonfish: Tang Fish, Yellow Tangs and other Surgeons
I like my yellow eye tang.
If you do go with a Tang, just get one!
