Well, as you probibly know, Damsels make poor community members. I have seen them kill several Ocellaris Clowns in the tanks at the
LFS. So I would highly recommend you stay away from damsels.
As far as filtration goes, YOu will want a Skimmer, and of-course Live Rock. Many people go with a Wet Dry Filtration system on their tanks, but that is kinda being phased out for more favorable methods.
Your current
HOB filter will not be nearly powerful enough. If you don't want to have alot of live rock, (and thats understandable, because your looking at about 500-600 bucks to do it right) I would recommend a large canister filter, the largest you can find. (about 200-250 bucks) I have a Magnum 350 on my 37 gallon that works well. I would not recomend anything smaller than that.
You will also want to be able to push around the water pretty good. dead spots are not good in a
SW tank. Look at investing in about 3 good powerheads. (maxi-jet 1200)
Of course don't forget the skimmer! A good protien skimmer works wonders to remove alot of the gunk. The Aqua C Remora is a great skimmer for a tank that size. (170.00ish)
thats about all I can think of right now...feel free to ask more questions.