I wish the VL GCP manual was more comprehensive but you can do lots with just the unit itself.
1) the GCP will work with any volume pedal or expression pedal. If you can find either one with a minimum level adjust, Boss volumes have this amongst others. You can then either use the expression pedal to go between solo and regular volume OR leave it up and set the patches on the GCP to either have the expression active or not, the rhythm patches have expression, solo are expression off ie full
2) you can program adjacent patches to send the program changes per device so if Torpedo patch 1 is rhythm and Torpedo patch 2 is lead and you also have a midi preamp and a multi effect
Patch A
Preamp program X
Multi FX program Y
Torpedo patch 1
Patch B
Preamp program X
Multi FX program Y
Torpedo patch 2
You can also change modes and have the top buttons assigned for individual applications, for example to change the Torpedo's setting
Midi solutions make cool boxes but the mapper is the model that requires the most programming knowledge.