Stagnant, I really enjoy this. I must say that despite some people's difficult posts, you must keep positive and continue with sharing your idea!
What most posters seem to not realize is that this would not ever be a part of Skyrim.. If this was to be implemented into Elder Scrolls, surely it would be in one of the next games. (I vote for Elyswer as ES VI) And in Elyswer, (if that was to be the setting for the next game), the game will be centuries into the future, where our character will NOT be the Dragonborn! (and dragons will probably be truly extinct)
Therefore, along with whatever storyline, this idea of becoming a 'jarl' could be used as a opportunity for our ES6 character to be close to the importance as the 'Dragonborn'.
Coming up with the money to fund such a city/province/village/hold/harem^-^ (whatever you wish to call it) is actually realistic. If the people of your hold were to give you taxes every now and then, as husbands/wives do, then you would be able to slowly-which is surely realistic-build your city from nothing to a loved/feared hold with a brilliant or atrocious reputation.
Also, the matter of leaving your town for an extended time is not very troublesome. I mean, unless your using console, you have to sell some stuff or visit your house to through your 'found' riches into your chest/safe...Where better to go than to your own village and improve the economy of it by investing things of such value? Besides, your second or third-in-command could handle the village as you are away.
My poor in-game hubby, I leave him alone for a couple days. (Surely, many others do the same thing.) And it does not affect gameplay.
So yea ^w^.
-I vote for Thieves Guild and Dark Brotherhood advisers which lives in your hut/house/mansion/castle....until night time.
It would be convenient for the TG adviser to be a fence. Perhaps you could hire them from the guild or sanctuary after a certain point of your town's development and your own position in the guilds.... Is there a certain guard doing open-handed deals without giving you a cut of the $$?--Your loyal DB adviser would be ecstatic to take care of her/him. (Wouldn't it be nice to have a DB adviser that reallllyy, in a comedic way, lovves to kill people, and smiles brightly as you ask them to take care of it?) Unique personalities are a must.
-Different available locations?
-(Similar to an idea previously given.) Perhaps you could overtake a rickety village(costs less at beginning) or start from scratch at another location? (you must have the $$$)
Keep confident, Stagnant.