Has already stated if you want to keep Damsels in any number you want to be in the Chrysiptera genus. Talbots, azures, etc.
@ca1ore has over 50 in his 450 gallon so speaks based on experience with regards to large numbers if you will. I've kept 3 Azures and 3 Talbots together without issues in a 40 breeder. The key is to have enough rock and mature coral so that they all have their own territory and safety space.
I think that is really important though. New tanks or relatively young tanks do not offer enough mature coral to break up the chase. They need places to sleep. Places to shack up with others if they bond/nest. And finally places that they basically retreat too when things go crazy. If you can provide a mature tank with good coral growth then you can put in any number of Chrysiptera Damsels. It will add a splash of color and speed which is a good thing.
Lastly on the Chromis front - they are cheap but more or less fight until there is only one left. It may not happen right away but they start with the smallest and weakest then before you know it only one or two are left. Damsels, at least when I go diving and run across a reef crest with them, there are thousands in a small area and when you breach the crest of the reef and look down, well, it is a very mature reef with lots of different corals and the Damsels just dart in, out, and around so quickly that there is no wonder why so many and so many hiding spots.
Good luck with whatever you do.