Dan,
I am currently building a large MFT (between 2-3x the size of the 1080). I started with a 1080, then bought the two long rails and connectors. I will make my own top using a template that I am in process of preparing. I plan to post photos when the project gets far enough along.
IMHO, all you need to make a custom table is four rails and 90 degree corner connectors. The rail hardware is also essential assuming that you want to be able to use the guide rail system to make square crosscuts. The fence hardware would be a great addition, or you could design your own fence system so long as you can adjust it and keep it at an accurate 90 degrees to the rail.
Believe it or not, one of the most challenging parts of the operation is boring the holes in the table top. I have decided to use a Festool 20mm router bit in the OF1400, although you could use a 20mm forstner bit (CMT, for example, makes one) if you design a system to hold it perpendicular to the surface with repeatable accuracy (there are a lot of holes!!!!). Or you could just save some time and buy as many as you need pre-machined from Festool.
I have decided to accept the challenge and try to bore my own. If I really screw it up, I can buy the Festool tops later.
So far, I have taken the 1080 top, attached it with tape to a 2x 4' 1/8" sheet of mdf, traced the holes, laid out center on each hole. Next, I plan to drill a 1" hole at each center (spaced 96mm apart). 60-something holes later, the template will be completed. With a 20mm bit inserted through a PC-standard 1" OD (7/8 ID) the OF 1400 will go to town and drill the holes spaced correctly and uniformly and exactly 20mm. Making the template is the hard part. I have decided to use Rockler's jig-it for 35mm hinge hardware. They make a 1" long shank bit that works (along with several other bit sizes) in place of the 35mm bit. In effect, it produces a portable drill drill press which gets the shank perpendicular to the surface plane of the material and should give repeatable square holes. I'm stalled at the moment waiting for the 1" drill bit to come into the store.
I'll let you know how that works out and post some pics when appropriate.
I'm interested in following your progress as well.
Dave