Can I play Red Dead Redemption 2 without an internet connection?

You will be able to play Red Dead 2's single player story offline, but not Red Dead online without a connection. As long as you buy a physical copy of the game, all you need to do to set it up is to install it from the disk. Typically, the game would install as you play it, but this game comes on 2 separate disks. This is why you need to install first, and play when finished.

No, you can't play offline because you have to start the game from Rockstar launcher which requires the purchase of the game.

No internet = No play. Even in story mode. Rockstar's Social Club has to launch the game (and with Steamworks). As for sticking with an older unpatched copy, I have no idea.