It is a great idea to add a refugium to your set up. Do not use halogen lights as these will overheat your tank and provide very little usable light. I reccommend the bulbs listed here:
http://reefcentral.com/forums/showth...hreadid=313318
I use these bulbs with great success.
You can run your fuge with a sand bed, bare bottom, or with the miracle mud. I think it comes down to personal preference as many have been successful using each.
In my opinion the best macro algae for a fuge is cheatomorpha. It grows fast, consumes nitrates, and will not go sexual like caulerpa.
As far as critters are concerned, you could put just about anything in there: crabs, snail, stars.
I hope this helps!