I wouldn't worry about pairings for the Plonk. 48 hp will NOT be enough space for this to work. Either you'll have to resort to a pile of very slim modules that are no fun to work with long-term, or you'll have to compromise on something essential.
Given the importance of MIDI here, my suggestion would be to get an Intellijel Palette...104 hp, preferably. With that, you can locate the MIDI interface in the cab's tile row (along with a number of useful utilities) and use the cab's USB for connection between it and your DAW, controller, etc. With more space, you can then avoid the super-tight spacings common with "Beauty Case" builds AND you'll get to have proper sections for sound generation, control, and modification.