you're supposed to cycle the tank with the live rock until the all your water paremeters are ok then add a fish. The damsel is probably going to die if you add live rock while its in there, but either way the damsel will die. you need to do more research.
the goby is 2.5 inches and the eels mouth is about 3/4 of a dime. I also heard that if you keep an eel well fed they usually dont bother your other fish.
Yesterday i saw a snowflake eel that was about 4 inches long and I was wondering if I could have it in my tank.
Its a 110g
it has:
a purple firefish
scopas tang
sixline wrasse
sleeper bullet goby
bluehead fairy wrasse
all the paremeters are fine.