Mainstage setup for keyswitches and multiple instruments

I don't know how to do what you are looking for.

I use lots of key switching in Logic but for live gigs with MainStage, I avoid virtual instruments that need keyswitches. The main reason for me is that I don't always remember which patches have keyswitches in the exposed range in the MS patch. So I'm often playing too low in the range and hitting key switches that I didn't know I hit. It's a nightmare to recover because I would have to open the plug-in window to know what it is set to and switch it back.

It's easier for me to switch my keyboard to a different MIDI channel if I want short strings, vs long strings, for example. As long as I can see what MIDI channel I'm transmitting on, I know what sound to expect.

I would reccomend you don’t split the keyboard just make sure there are no pitch range conflicts in both sounds and key switches

I agree that using key ranges is error prone. I once used a logidy UMI3 with three foot buttons to switch horn articulations. It was error free for me. That device allows you to define note #s for specific buttons, so I didn’t need the Mainstage articulation sets. They might help you however, depending on your rig: