Hi there,
you might want to check this thread - your challenge is pretty similar to my original use case: keep a PC in a rack backstage and have a “light” solution with your keyboard rig.
I’ve been there with the small monitor velcro’ed to the keyboard, but these days I prefer a 10 inch touchscreen mounted on a separate microphone stand - reduces the vibrations from my hitting the keys 
In my new solution, I now use a KVM extender with the touch screen. The extender runs HDMI and USB over up to 50 meters of Cat6, so my rack and (small form factor) PC can sit safely backstage and connect to my keyboard rig. With this extender, I can also connect my keyboards with the PC via the same cable - no noticeable latency.
So one little box sitting on top of my lower keyboard, connected
- via HDMI to the touchscreen
- via USB to the screen (for touch)
- via USB to both keyboards for USB MIDI
- via USB to a trackball on my keyboard (in case I need a mouse-type device to do some twiddling of my setups
I can control the Cantabile PC via touchscreen, mouse and the two MIDI keyboards. No further connection needed beyond one Cat6 cable between my stage rig and the backstage rack. Not quite correct in my case - I have a second connection: a small multicore for microphone, guitar, in-ear and/ or keyboard monitor.
Works nicely in my studio / rehearsal room so far - yet to test it in a real live environment, but promising so far.
Cheers,
Torsten