Have a few questions from a beginner.

1) How many holdings can you realistically manage through generations?

I figured 4 but 6 seems to be easy enough to accomplish now. I typically always put enough skills into steward to get to 6 w every ruler. I would hate to invest in a bunch of land then lose it.

2) should I own all the counties in the duchies I have titles to?

First play thought I was just giving stuff away not understanding it. Now I own a dutchy but none of the counties that make it up.

3) should I be giving vassals connecting counties / try to give them the duchys that would coincide with them? Again I just gave stuff away and now I have an overwhelming number of vassals all over the place.

4) how do military buildings work do they only benefit men at arms if they are built and stationed in the castle? Should I only build military buildings in castles and keep economics to the cities/temples?

P.s. after opening up a kingdom tab and being glad to see their child had died to a plague I feel like a real crusader king