Thanks for the ideas, for now I am still reading some guides/random stuff from the wiki, and tomorrow I will start playing.
I don't have expectations, I remember when I started EU4 how many times I lost armies because I forgot to move the army slider before the war started and my morale was low when attacking, and how many mistakes just killed my games. So first I want to read a bit, then play something easy to get acknowledged with the mechanics.
EDIT: Building an excel to have on the right screen when playing so I can quickly read important things.
Something like this
https://prnt.sc/u7raa9
Nice spreadsheet!
A few tips:
The Imbecile trait makes characters as likely to spill the beans on plots as Drunkard does. Slow and Dull also increase the chance, but not as much.
If you aren't beyond using exploits, an easy way to get money is to search for unmarried men with no dynasty (no great family) in the Character Finder. It may take a bit of time to find, but you can often find deposed mayors here, with hundreds or even over a thousand gold. It takes a while after game start for that to happen, though.
If there are no heirs (like a deposed mayor who has no family and no dynasty) then an unlanded's gold is inherited by their liege lord. It's often easier to murder than imprison and banish, which you can take advantage of here.
To change the culture and religion of imprisoned children you have to put them in house arrest, not in the dungeon or oubliette (they are in the dungeon by default when you capture them). Children in the dungeon or oubliette have a separate chain of events.
One advantage of children in house arrest is that you get the chance to change their culture and religion without needing to set the appropriate focus, while you need either Faith or Heritage on free children. You can educate house arrested children any way you want and still control their culture and religion.
However, remember that children's culture and religion can only be changed between the ages of 6 and 12.
You don't actually need to assign a tutor to children you have imprisoned - they will have you as tutor by default, without taking up one of you two spaces for wards.
Tutors won't always change the culture or religion of wards, but if you are the tutor then you get to control the choice when it pops up. But if you have a lot of child prisoners the number of childhood events popping up can be annoying.
PS. I'm not sure what you mean by divorce for money? If you were inspired by the CK3 video then unfortunately that won't work in CK2. After your first wedding your character is marked, and you get no more choices between Prestige and gold upon marrying someone after the first time.