I would agree that the two master setup within the same faction would be fun. As far as the soul stone pool size I think it should stay in place to help those that have a limited number of models as well as hopefully making the setup times between games abit quicker with a limited number of models. The upgrades should either have their own soul stone pool or none at all, and I would lean towards not having a limit on upgrades.
I realize that I have answered the asked questions but I would like to interject one other thing. I played in last years walpurgis and had a blast but the only frustrating thing was the time limit. I had about half of my games end on turn 3 and that is right when the game begins to get good and the decisions become big. I would like to see a little more time figured in for each game if possible, but otherwise it's a great event and I am looking forward to it again.