Will it be possible to buy/ rent out houses? That or invest in towns, farms, or other businesses.

No one knows. But it's a pretty good idea as long as it isn't like Assassin's Creed 2 or Fable 3, where you get waaaaay too much money from it.

I agree a balanced system for income would be nesicary

Player owned houses would be nothing new for TES and neither would investing in shops. It would be a nice if not overly important adittion to see these ideas expanded and implemented in a realistic way. The economy issue in general, for me, is something that they really need to look into. The ease with witch you could make money in Morrowind and subsequently buy training (you could reach lvl 70+ in a mater of hours) must not be repeated. Oblivion was a slight improvement in that area but again, it was very, very faulty.

What about investing in certian trade routes or caravans? Maybe your investments would make it safer for goods to be moved from town to town or find a new route to a far away land that would bring in exotic foods, weapons, and clothing/ armor.

In order for all of this investing to work realistically, a bank must be in Skyrim for the gold to be depositied to.

A bank would also open up more possiblities. It would be fun to rob said bank, but it could also be a place to track all of your investments that way you dont have to go from town to town to make sure that every thing is running according to plan.

Most important of all, you must have the ability to spend. Items that are way too expensive give you incentive to make money. Making money for making money's sake won't work.