I've also been researching sumps/refugiums a lot lately, and have come across variations on this model. There a are a few things I think you should consider:
- you may have to deliberately over feed the display tank for the catfish to get enough food to survive. Otherwise, the occupants in your display tank will simply eat all the food. Some potential risks of this are that you'll have fat, overfed occupants in your tank, higher nitrates than you'd otherwise obtain, and possibly an increased likelihood of your pipes becoming blocked.
- you'll probably have to remove the filter bags in the first compartment otherwise the food will probably never reach the fish in compartment 2. It'll be trapped by the filter bag.
I think it'll work as a sump/refugium, but probably not as a way of feeding your catfish (I presume you mean cories) adequately at the same time. But bear in mind I've never built or used a sump. These are just my thoughts based on what I've read. Wait for some of the more experienced guys to contribute before you decide - I'm sure they'll have more definitive feedback for you.