Software is almost all on www.unna.org , which for some reason is misbehaving but persevere (and avoid the torrent in favour of http d/l).

Networking cables/ hardware available here — in quantity — but you might want to look also at pcmcia ethernet, wireless and such options as well. I gather than even bluetooth can be done, though I haven't gone there.

The Newton is fussy about what it will accept in regards to such new-fangled add-ons, but the solutions work rather well once you get them going. For bootstrapping, mind you, you will likely need your 7100 and a serial cable, or else some phonenet/ localtalk hardware.