Am I overstocked
 

Just want some opinions, to see if people think I'm getting overstocked. Currently, I have in my 180g mostly sps: 1 mimic tang, 1 small 2" Yellow tang, 1 Large Copperband, 1 perc, 1 blue damsel, and about 10 green chromis. I want to add one more big fish like a purple tang, and a couple of small fish like gobies. Any opinions. Tank is well matured, and my skimmer will have no problem keeping up with a larger load. Also all fish get along great with each other. So Far!

If it was a 33g, 180 is a big tank.

I think you are fine and can easily add more fish particularly if your skimmer is able to keep up with the additional load of bigger fish and you have sufficient live rock for biological filtration.

No I don't think you are overstocked at all. With a large skimmer like you say and a mature tank I'm sure your system will not have any problems with the small increase in bioload.