Lots of good questions Dan. I don't have any of the snakes on your list, however, all the snakes on your list feature in my list (infernalis is top of my list and I hope I'll be getting at least one this year), so I thought I'd let you know that you seem to have impecible taste.
Others have said the same thing, but in my experience garters have their own personalities and snakes of the same species often have different personalities. The species I have that are the same species are opposite sex, so I don't know if the difference in personality is down to differences between the sexes. Observations of our 9 are:
T. radix - male and female both friendly and mellow.
T. e. cuitzeoensis - male more skittish than female, but both are quite shy and easily spooked.
T. marcianus - albino and normal female are both friendly.
T. cyrptosis - both are quite reclusive and shy feeders, the female is less so than the male.
T. s. parietalis - female is really active, friendly and easy going.

Hope this helps.