jwt said it, the only thing is wiht the damsel, i would not consider a ff unless you are returning the damsel
in either case, i myself like blennies scooters and algae(aka lawnmoer or sailfin) are cool and fearless(pretty much) not aggressive so would be ok with ff or damsels
as far as how many, that will depend greatly on which fish it is you get
do you want something something aggressive, or peaceful??
HTH