What Fiefs are best to give to Vassals?

[Raga]

My first fraction were Nords, but after a quarrel with Ragnar who didn't want to give me the castle I had captured I made my own fraction to keep it.
I had Reyvadin, Tilbaut Castle and Dramug Castle
Lately Nords were attacked by the Rhodocks and lost (Lord Migrated to Rhodocks) Khudan? City (the one at far east of Vaegirs).
I also started the war with Rhodocks and captured Khudan.

I cannot handle so much fiefs, so what is the best (economic wise) way to split them among Vassals?
What type to give away is the best?

Additional question:
Is there any way to advance (level up) followers that were turned into Vassals (Alayen has no "show me your skills" dialogue option any more)?

 

[zParsifal]

Additional question:
Is there any way to advance (level up) followers that were turned into Vassals (Alayen has no "show me your skills" dialogue option any more)?

Not in Native, but there are some mods that you can use with your existing saved games that will let you do that.

 

[Captain_Octavius]

Towns are the most profitable in form of Tariffs, so I usually keep two or three towns myself. The rest I give to my vassals. Remember that it's better to have a smaller group of vassals that own 3-4 fiefs each, than a larger group with only 1-2 fiefs each. Castles are best given away, they barely provide income so they are just extra garrison costs. There are a few castles that you should keep and use as honey pots (small elite garrison to lure attackers, then jump in with your own army and have an easy day massacring them).

 

[Raga]

... Remember that it's better to have a smaller group of vassals that own 3-4 fiefs each, than a larger group with only 1-2 fiefs each...

What is the chance of Vassal betreyal?
Can I assume that Vassal with good relations with me will never abandon my Kingdom?
Are Followers turned into Vassals more loyal than normal Lords?