This has been built as a single player game, and there are currently no plans to add multiplayer.
Controller support would be really good, but it will likely not be soon. Inventory management will need some significant effort.
I think multiplayer, even co-op will be very interesting, especially if you'll add bosses. Also I think it'll be cool too see hub more alive.
I tried to make co-op game time ago and that was damn awful try. I believe you should finish the singleplayer first and start making online features AT THE END of developing. I think it'll be the right way...