Hi,
I don’t have access to my workstation now to test this out but what comes to my mind is you may have the same MIDIIN3 (SLMIXUSB) input defined for “Track Quick Controls” - which can also be found in the Cubase Studio Setup menu. So your same MIDI input goes to both Mackie control and these quick controls - and if Mixface sends by default CC1 message, it happens to be pitch bend. Test by removing MIDI input from quick controls.
For (3), button presses on Mixface do indeed send midi notes. You need to select which MIDI input you want to use for your channel (instrument track, or MIDI track). By default the setting is “All MIDI Inputs” so all MIDI activity ends up as your channel input. Select your keyboard as input, or whatever input device you are using.