Macro algae need light and nutrients to grow. The more light the better. Some people use their old MH bulbs over the refuge. Others use the HD bulb you refer to. They both work. If you are not getting the growth that you want from your macro algae, it is easy to increase your lighting at that time.
I would not prefilter your water to the refuge. There is no need and it is one more thing that can go wrong or needs maintenance.
If you are using your refuge to grow pods, etc to help feed your fish, then don't forget to feed the refuge area. If I feed blender mush to the tank, I also add a little bit to the refuge. If I feed flakes/pellets, I also add a little bit to the refuge. I have noticed a large increase in the number of pods since I started doing this.
As for type of macro - here is a thread that notes some of the macro algaes commonly used with comments -
http://www.reefcentral.com/forums/showthread.php?s=&threadid=349241 Personnally, I grew grape caulerpa (racemosa) for over a year. I used reverse lighting (opposite the display tank for most of that time) with no problems with it going sexual. From my reading, I believe that sexual reproduction happens when a plant is stressed (not enough room, lack of nutrients, etc) as the plant tries to ensure that enough "seeds" are spread that it will continue growing where conditions are better. I always pruned when the tank became 3/4 full and increased the flow until there was enough movement so that all of the caulerpa ball was getting some light. Then I decided to add other macroalgae - mangroves, red and green tang heaven (graciliaria), ulva, caulerpa prolifera, caulerpa paspaloides (feather caulerpa) and some chaeto. Nothing grew very fast and the feather caulerpa died. I removed the red and green tang heaven and ulva. They are now in a special algae grow out tank so I have enough to feed the tang. I still don't have great growth but everything seems to be living. There could be an issue with the plants excreting a chemical to prevent the other macro algaes from growing. I am still researching that.
I believe that Dr. Ron once posted that a sand bed had to be about 25 square feet to be effective. Your bed won't be big enough to use as a nitrate processor. Your sand bed will be big enough to promote the growth of worms, etc that will help keep that area clean. If you decide on caulerpa prolifera, it needs a sand bed to be rooted in. I would put sand in there (I have sand in the bottom of my refuge and also sump) to promote the growth of these bugs, etc.
I have a couple of hermits and a turbo snail in my refuge for clean up.
I do recommend reading this article -
http://www.advancedaquarist.com/issues/aug2002/chem.htm
Vickie
