Hey Kristian,
I’d very much encourage you to take the plunge - I’ve been pretty much where you are now (plus a bit of guitar kit in addition to the keyboard rig) and since moving to a very lean Cantabilized setup, haven’t looked back!
Just a few pointers from looking at your proposed setup and my own experience:
Your current PC3x could also be a useful master keyboard for your Cantabile setup - great keybed, lots of sliders that can be useful in Cantabile, more switch / pedal inputs than most alternatives. You might consider keeping it just as a “dumb” master keyboard (even though it’s a bit on the heavy side). I’ve looked at lots of (lighter) alternatives, but nothing has really convinced me to move away from my two Kurzweils
Second, you might consider moving to a leaner PC setup: instead of a full rack PC with ADA8200 and UPS etc, you could pretty much get the same (if not more) from a middle-of-the-road performance notebook (gamer laptops!), plus a multi-out USB audio interface like the MOTU Ultralite mk3 (10 individual outputs). No need for a UPS - laptop can run on battery if needed - and far less to shlep around - will all easily fit into a sleek laptop bag. And a backup solution is also easier - far easier to carry a second laptop than a second 6U rack with all your stuff.
I run my setup on an Acer Aspire Nitro VN7 gaming notebook (quad-core i7), and I’m super-happy with the performance I get. I used to bring a 2U rack case with my RME Babyface plus an ADA8200, but with the MOTU Ultralite, I get sufficient outputs with less to carry; and the latency is certainly good enough.
Regarding display/keyboard/mouse: I rarely touch my laptop during a gig - mostly, it’s stepping through pre-loaded setlists, and this is easily done with two dedicated buttons on my PC3. The only thing I need during a gig is a small 7-inch HDMI display that shows me the currently loaded song and song state (Show Notes View).
You can see my setup here: Show me your Cantabile Rig! - that’s still with the Babyface/ADA8200 (the mini-rack at my feet).
An even smaller setup (when there’s a decent weighted MIDI keyboard already on-site) is here: Show me your Cantabile Rig! - this one includes my MOTU Ultralite.
BTW: great idea keeping track of song changes using git - I’ll integrate this into my setup ASAP!
Good luck with your Cantabile journey!
Cheers,
Torsten