Brent, funny you mention that, I was already thinking about putting the CO2 tank in the stand. There is a lot of space available (72" x 29" x 36") and the only other equipment destined for it is the CL (Dart, OM 4-way, plumbing) and perhaps a separate refuge for pods, as a pair of mandarins is on my wish list.
With the arrangement I have, a drop-in chiller may be a great choice. I hadn't even considered it before. The compressor will go in a separate room adjacent to the equipment closet and the sump will only be two or three feet away. I haven't yet finalized the sump design so I could be a compartment just for the cooling element. Not only will this simplify plumbing, but it will also eliminate the need to periodically clean an in-line chiller. Most of the negative things I've read about drop-ins are the limited distance between compressor and sump but this isn't an issue for me. I'd be able to use a smaller return pump (like an Eheim) without an in-line chiller in the return circuit also.
I have to play with some empty boxes to see how big a sump I could get into the existing cabinets as I don't really want to cut the face frame. I certainly could locate the gravity-fed, recirculating skimmer in the sump if there is room. This would again simplify plumbing and also help prevent water from leaking onto the floor.
Thanks again for your great ideas!