Get the column choice right first:
Go to as many real estate blog sites as you can before you make a decision on number of columns. The large text column is one, and there can be one or more columns on the right, left or both.
See how others are using columns, and how many "widgets" or "plugins" you might use before you decide.
Now consider the header size:
The "header" is the top part of a WordPress site that is visible on every page of the site in most cases. Too many "real estate" themes have some large picture of a home, kitchen or city scene as their header. Think of the smaller netbooks and mobile computers, and you'll see why I think you shouldn't be wasting valuable screen space on a repeating boring picture header.
Look for a theme that meets your other needs and doesn't use a large part of your screen space for a photo. There will be less scrolling and more information "above the fold."
Unless you want to learn CSS, choose carefully:
I'm talking about the colors, fonts and general styling of the site here. You've decided on columns, and you're hopefully going to choose a theme that makes efficient use of your screen space. Now just look hard at colors, fonts and other style options. Be happy with the theme you choose, as it's a real pain to try and go into the code and change these style options. You can create some really messy situations.
Take your time choosing a theme and try to stick with it:
While you can change themes later, try to get one you'll be happy with to avoid problems that sometimes come with a theme change. This will get you to a point where you can begin to categorize your future content and even creating content.
The simple steps in this article should lead you to several choices for your first theme. Actually, install several, as you can switch between them early on to make a final decision. Once you have your theme activated, it's time to move on to setting up your navigation and categories. Then you can begin to create content.