Is there room for anymore fish?

Unfortunately, that's most likely going to cost you someday. No matter how well-maintained or stable a system is, you need to consider that the newcomer has NOT been in that nice system. It has been in the chain of custody with multiple stressors and possibly poor conditions.

Back in the old days, I felt the same way until a new fish killed almost every fish in the tank due to a crypto (it was a reef, so not even a remote chance of treating it in situ). The real bee-yatch is that I don't even LIKE yellow tangs, but there were some exceptional-looking specimens, and my ex did like them...:-/

Peeps are just trying to save you some headaches.