That’s pretty much just what I do-- Hammond XK1c is organ/multi-purpose 2nd board, and the Keylab is my Piano/Clavi. I have a setup where it’s routed as a second manual, but that’s pretty much just for me practicing and trying to learn “real” organ skills. The keybed is not great for organ feel, in my very un-informed opinion, but it’s a fine slightly-spongy piano bed for me.
I have the controllers on the Keylab mapped to transport, song states, default sounds, etc. (there are a ton of buttons to map!), and I have the sliders mapped to small volume adjustments if I need to do a bit of one-stage mixing on the fly.