A couple of sorta meta-gamey questions!
1) You can in theory get negative relations with your faction, if you didn't start it yourself, since joining only improves your faction relation by 12 points and you retain the ability to jump into battles against your own. Are there any repercussions besides the obvious ones, like not being able to enter faction fiefs? I might join a faction early to grab a walled fief and start custom knights order, for instance, but at the same time I don't really want to make my faction too strong, so the ability to attack an important lord could be handy. This of course raises a bunch more questions, so if anyone tried experimenting with this sort of thing, I'd love to know.
2)You can in theory get negative relations with your own order. Do you get kicked out if that happens? If you're grandmaster, will you still be able to enter Order Stronghold? My guess is no, since it's faction aligned, but you never know.