Wow that's a lot of damsels, good luck getting those little suckers out. As for the fish load, you will want to figure an inch for every five gallons, that is a mature fish length not how big it is when you get him. For fish only you shouldn't have a problem with most any fish, just check to make sure they will all be compatible, and add them slowly over time as to not overload the system. Patience is key in this hobby. Good luck