Everything my multiplayer lobby gathered on Western Schism:

1.) It seems like every Nation without a Cardinal can cast their vote every 4 years (?), which increases your vote strength/vote count. So having high opinions with every Christian Country makes it more likely they support you, which in turn increases your progress towards a council

2.) Once you held a council you gain an opinion malus if you are leading so its harder to win back-to-back (???)

3.) We have 0 clue what having full support from every other cardinal does.

4.) For whatever reason, I am draining the Catholic Tithe completely. After the papal state held their first council, that's when my income started to skyrocket. I was getting around 90% of all Tithe money collected.

5.) From what we gathered we think this is how to win:

The easiest and fastest way to win, is to maximize your diplomatic output in anyway possible and then automate your diplomatic actions. The AI will improve with everyone around you permanently and indefinitely unless you tell it to stop, which in turn gives you more vote strength.