I personally believe that you should avoid repicks unless theres a super valid reason to. If teams are unbalanced (which shouldn't happen that often with experienced captains, but as a theoretical) the game should be over pretty quickly and its not worth the headache to try and balance teams mid game. (unless theres another reason to bring in other players, like if we need a sub)
Probably team dependent, some people like to sweat out and do well while some are more casual. What i do want to make clear is that if you are going to meme or do deagle only or something, PLEASE make sure EVERYONE on your team is okay with it before doing so.
I don't think we need a set day for it, but if majority agrees it should be fine to pull them out occasionally imo.
Not sure what would happen. They're pretty controversial guns in general so i think its better if they stay banned, but i don't have strong feelings either way. People do freak out if you get killed by it though, which is pretty funny.
EDIT: forgot this one oops
If they have a legitimate reason for leaving, nothing. If someone leaves repeatedly i wouldn't be opposed a ban/blacklist.