Having been stuck in a 3-player game many times, I really like your rules. We have run into problems with strats and schemes before, mainly the Victoria's only scheme. We typically just make changes on the fly as they come up and I will be using your guide as our start.
And sure, many times a 3-player game turns into a 2v1 at some point, but I just call it cross-faction hiring, the enemy of my enemy is my friend.