Yep, 2 midi cables, one long and one short

the idea is to assign each unit to a number e.g. ADA is unit 1 and G-Major is unit 2. Once that's assigned, you have to program the midi board to do patch changes, which is what you just described. It's a matter of assigning the footcontroller's "patch" to change a certain unit's patch. For example:
FC patch 1 = ADA patch #1 [distortion] + G-Major patch #15 [delays]
FC patch 2 = ADA patch #2 [clean] + G-Major patch #3[delay + reverb]
FC patch 3 = ADA patch #25 [hi-gain] + G-Major patch #100[delay + Midi assigned CC for delay rate]
For the expression pedals to work from one device to the other, you have to assign a CC on the pedal and the unit. Essentially, the idea is to have Expression Pedal 1(CC 1) "linked" to a parameter in the G-Major e.g. Delay rate or something else[refer to Mod Assigners]
hopefully ya get the gist
Reg