I'm not sure there is a rule. The Rangers actually have a Hall of Fame. I am not sure what the length of time one has to be retired to be eligible, but Juan will certainly be elected once he is.

I doubt the Rangers will retire his number. They only have 3 numbers retired. Nolan Ryan (34), Johnny Oates (26) and Jackie Robinson (42, like every other team). The Rangers haven't done that a lot. Albeit that might be because they haven't had anybody really worthy of that great of an honor until the mid-90s teams.