I apologize for not reading your whole post but stand by the suggestion. If someone was new to guns and looking for a first I'd suggest a .22 for learning safe handling protocol. If you want something with a thicker body I would suggest something pituophis(like a pine or bull) but your maximum cage dimensions wouldn't do for a large, active colubrid. Out of your list, anything but the ball python would be pushing your original spacing limits. Otherwise, of those I'd suggest the JCP solely on their being fairly cold hardy. I don't think they're like a chainsaw at all. They can be defensive as youngsters - many species are - but generally calm right down with a bit of size. Also, if you haven't, check out some of the myriad of kingsnake options.