The Wayfarer's Inn

Well, following the discussion on Grand Duke/Duke/Archduke I ended up breaking from the way oD&D (RC/Companion set) handles nobility titles.

IMC it now goes like this:
Emperor:Reigns over semi-independed dominions and his own lands. More or less like a king that takes salt tax from other kings.
King: Reigns over his nation.

Kingdoms are broken up to Duchies and Counties.

A duchy may have counties in it and it may not. It may also have baronies in it, and it also may not. Since Duchies IMC are large (about 30-40000 sq.miles or 80000-120000 sq.km) they usually have baronies at least.
Note than IMC the king usually rules directly over some part of his kingdom as large as a duchy.

A Count may be beneath the Duke or directly under the King. A county may have baronies if the Count wants.

Barons IMC swear fealty to a Duke or Count. A few barons may be appointed to rule parts of the lands the King has kept for himself, but this is rare.

So it is more or less Kingdom-Greater domain (County/Duchy)- Barony.

Kingdoms that have been established recently have large dominions with a few large baronies. Older kingdoms have smaller dominions with more baronies as the Various lieges broke up their lands to award generals, relatives of the king etc.

If the Liege has more than one sons the younger usually become high ranking officials (generals, mages, diplomats) and inherit a small part of the family fortune but usually not any barony or something. They may be rich nobles that just sit in their mansions or they may also have some offices. While many such nobles are ambitious and plot for power others are content to just live in luxury without any serious work to do, like living in life-long vacations.
IMC there is a 5-10% of firstborn sons that forfeit their chair to the younger brother or even to their sister's husband after the father dies, so they can be free of the burden of rulership. Some are just lazy good-for-nothings that decide it suits them more to party and eat all night long instead of ruling. Others are magic-users wanting to be free. Others (the extreme minority) just agree that their brothers are smarter/better rulers and they just become advisors.
Question: Is that a logical percentage? I mean there are examples of modern rich people that are content to avoid working leaving the business they inherited on assistants while they live on the profits.

Hmm... yes but if you like to go party for the rest of your life ... and you have a brother that seems a bit ambitious, what you do? Have him assassinated before he assassinates you? What if you love your brother and he loves you with all the shortcomings? I mean, yeah he likes to rule and you like to go hunting... so? He's still your brother. You either assassinate him and go on hunting and partying leaving the state to assistants or live with fear of being assassinated?

OK... Thanks for the info. I never understood nobles very well. How many of them appointed regents in the High Middle Era?