You go to the gym to lift. Not to talk. You may talk shortly if it is related to something you need to continue your workout. Apart from that you do not talk. End of story.

I used to authoritatively state rules that existed in my own head. I no longer do this.

I always liked busting through the little social candy shell in the gym. Offering to let people work in on a scarce piece of equipment could lead to chit-chatting about whatever. It's nice! When you have about 3 minutes to rest in between sets there's time to let someone else work and talk a bit.

Varies wildly. Some people are there with this attitude. For others it's more of a social time with occasional breaks to do a workout set.