I have never made one of my companions a vassal, but because right now a bug is affecting me, im considering it.
Bug: http://forums.taleworlds.com/index.php?topic=340527.msg8100030#msg8100030
But there a couple thing I would like to know first:
1- All I have to do is give him a fief?
2- Will he keep leveling up when he fights?
3- Will I be able to assign his skill points when talking to him?
4- Is there any way to make him come back to my party and leave his territories?
5- Can I change the items he uses once he is a vassal?
6- Will he have any other difference to the "normal" vassals?
Thanks.