If you know your ISP, the best thing to do is try to schedule a face-to-face meeting with their management and security personnel. Be prepared to explain Tor, its essential function, and both the pros and cons of running an exit. Then listen to their concerns, and try to address them. Ultimately, if they’re not on board with the basic idea of running an exit, none of your other questions matter—because they’re not going to get paid for the hassle of running Tor. They have to be willing to host your exit purely for the sake of the warm fuzzy feeling of knowing they might be helping some oppressed soul somewhere, or at least annoying the NSA and its international counterparts.
Or, find an online “faceless” ISP that specifically permits Tor exits in its AUP.