I’ve never tried with detent encoders.
See here for making those work.
Not really anything simple. The board is pretty specifically wired for that Newhaven display. To replace it you’d need to find a similar but larger SPI display and manually rewire things. Then a bit of mucking about with linux settings, maybe drivers, etc. Messy.
You could try to use HDMI out from the pi, but I don’t know specific settings to make that work well. On a pi4 HDMI will take over the norns display output. So you could try starting there perhaps?
EDIT - you could also look at the “official Raspberry Pi 7” touch display" – it uses the direct display ribbon connector and leaves the GPIO pins free, so it could work. But youd still need to do some hacking to get the framebuffer to display in the right place.