hey hey! I moved your post here, as it better fit the topic 
crow is the easiest way to, yes. it was designed to speak directly with norns and integrates into the system very easily (in the CLOCK menu of norns, there’s an option to send clock out through a connected crow, for example). but as @Gexex shares, you can use any class-compliant MIDI interface to send data from norns to your eurorack system.
no, grid connects directly into norns through one of its USB inputs. norns speaks fluent grid, arc, HID, and MIDI 
50/50 – lots of apps require grid for full usability, but many do not. barcode, patchwork, and lissadron are just a few quick examples of deep scripts which can be used without grid (barcode + lissadron don’t use grid at all!)