I agree that you want to look at the range of skimmer sizes that you may want in the future. I have changed skimmers 3 or 4 times (I have come to believe they are all POS's...but that's another story).

I eventually had to do some major modding of my sump to make them fit. My sump is made of acrylic and I spent a day standing on my head inside of my stand cutting and dremel-ing to remove one of the baffles entirely. Nothing like the fumes of melting acrylic in a enclosed environment!

What I have learned regarding refugiums...try to design it so there is a fair amount of flow (this may mean smaller so it is compatible with your throughput in your sump). Ideally, I think a refugium should be shallow...realizing that this configuration doesn't typically work with how we normally configure our sumps. My reasoning for a shallow fuge is that macro algae likes light and water flow (Q=VA...shallow will increase the water velocity). Also I have found a deep slow refugium to be a detritus trap and at best the macro algae uptake may equal the amount of detritus decomposition in that area.