I like all of your ideas it would be great, I would like to pay tax. I want a huge estate or castle too it would be great if I could have one on the outskirts of a city sitting on or by a mountin or by a waaterfsll or by a mountin with a waterfall, and then you have to pay the tax or pay the price or kill the gurads after all it would be your call...

I always wished that the stronghold dlcs for Oblivion were more centralised. It would have been awesome, in my opinion, if the Vile Lair dlc had been beneath the Imperial City instead of on the edge of the map. The hidden entrance to Vile Lair should have been in the imperial sewers. I hope such would be the case in Skyrim.

I think you should be able to buy just about any house, business, or ship that the owner is willing to sell. See my http://www.gamesas.com/index.php?/topic/1160987-skyrim-traders-guild/page__p__17038708__fromsearch__1#entry17038708 thread for more info.

i like the idea of farms, stables and inns etc

i never used the properties for anything less than storing items but as places of business or activity give them more purpose
example say you buy a small cottage in the country side you could get some chickens, at first un-penned with little benefit as wild animals eat them and people thieving them and so on, as you level up and so on you get fences and bigger animals like swine up to cattle where you have to have stone walls built to keep them contained and maybe employ a local to manage the property, like wise with a property suitable for an inn, they could also tie in quests at different levels of development