I had a striped damsel that was with us from day 1. Been through everything- cycling, algae blooms, power outages, ick outbreaks... you name it. When we consolidated our tanks to the 240, I knew I was gonna want and get some other fish- and he was already, justifiably so, extremely territorial. So I almost didn't put him in- but....seniment won out and I put him in. I had fish from a 100, 75, & 20g., and put them all together in this 240- plenty of swimming room, plenty of hiding places, plenty of spots where they could "claim"... but no, he wanted to chase and nip at all the clowns, two of which came from his tank and had been fine with for 5 years or better. I added a coral beauty and a bi-color angel- he had the coral beauty chewed to pieces. It's a long and quite humorous story of our endeavors to get him out of the tank. But we finally did on night, or morning- about 2:00 a.m., after half of my carefully aquasculptured rock was in rubbermaid tubs again, got that little sucker out. He went temporarily into the sump, till we could take him and a big Clarki Clown to the LFS
and trade in. I still wish I'd kept maybe the 20 gallon to keep the two of them, because we did have them for so many years and they were quite fat and healthy... by the way, the striped's name was Sadaam, if that tells you anything.
So... all that to say this- damsels are very cool fish, but if you want to add different tankmates later, especially ones that about the size of damsels, they probably won't get any rest! I still want to get another 15 or 20g. just to have all kinds of small damsels in. They are cute and funny.