Marc, how much height do you have between the floor and the tank?
38" from concrete to plywood.
How much space are you planning for the refugium and return areas? Have you decided on a flow pattern for the sump? e.g. skimmer-->refugium-->return
I've really not decided much, but I'm dwelling on the layout from time to time. What happens with me is that I think about it gradually, and wait for everything to fall into place. Then when it does, I'm able to put it to paper, verify my design, and build it. This is a method I've been doing for many years, and it has worked out well. I drew a couple of very rough sketches of some of my possible ideas, but that's about it so far.