I'm going to try this for sure.
I have a few questions.

1)Can I let a faction hold only 1 province, surrounded by my provinces and no sea access to ensure they won't attack someone?

2)May I use spies/assassins?

3)And i have heard that global reputation drops over time if you're playing on VH. Is this true and how do you encounter this aside from being at war with everyone and releasing prisoners/occupying cities?

I'll post screenshots but first I must find time to try this challenge.
Stupid school

I think it will work the best with Hungary.=> fast access to Middle east and jerusalem/antioch. You give baghdad to Vassal-turkey and you will get no jihads/crusades which will destroy your vassal-alliances.