As this may determine which version I end up settling for.

Theoretically, yes, in practice, not so much. GoG's version seems to lag behind Steam's version by a bit, and you'll not be able to connect when the versions don't match. I don't know if steam users can select a beta channel to avoid forced updates, but I'd expect a bit of work or some times when multiplayer with steam just won't work.

I tried it yesterday with a friend. He has no option to stop Steam from updating.

I'm at the point where it's more convenient for me to buy the game on Steam, because I can run steam on my linux machine, but not GOG Galaxy.

Yesterday I actually tried playing with my friend on steam and it worked without much trouble. Only our farm dog was glitching out a bit lol

i played with my friend for a whole in game season, no problems except a slow map refresh rate

Is there a way to get the game to save the IP number for a Direct IP game? I have to retype the same IP address every time I want to join a game.