It's entirely what you want and what you gain from research, everyone has differing opinions on what works best, etc. IMO, and this is a big IMO, the best refugium would have a DSB (at least 10 inches, if not 12) for anaerobic bacteria, etc. this would be to lower nitrates as well as keep other things in check, a pattern that has been noticed in my local reef club, is that sps in tanks without DSB's does not do as well and tends to bleach more often. Also, tons of macro algaes, many different types, just bunches of at least 3-5 different types of macro algae. Don't ask me why I think different types will help, I just do
, I think that different types will help better, not necessarily noticeably though, with different things. This may be wrong, but it couldn't hurt. Be careful with your macro's though, do plenty of research, some spread rapidly and if they get into your display, you could end up screwed with a crap load of macro where you don't want it. One species of caulpera is known for this especially, but I don't remember what it was. Also, I would put a conch or two in there along with a sands sifting star or two to stir up the sand bed. Absolutely no fish though because they will eat the pods, and I think pods are one of the biggest advantages of a refugium. I don't necessarily see the use of LR in a refugium as you should have plenty in the display, I would however throw a couple medium-small pieces in there for the pods that are in the fuge.
Keep in mind that this is MY ideal fuge, that doesn't mean you can't use it of course
, what it means is you have to do your own research to figure out what you think is best, everyone has different opinions when it comes to a fuge, and there's no "correct" way per say.
In Short: My IDEAL fuge would have a deep sand bed of at least 10-12 inches, a couple of conches or sand sifting stars to stir up the surface, several different types of macroalgae, and NO fish or predators to eat the pods and macros. It would also have several pieces of medium to small LR.