The biggest concern you need to have (unless you plan on hauling around lighting equipment, which is a pain in the #$^&&, not to mention a hassle when dragging it through someone else's house and knocking over Grandma's urn.....) is a camera that does well in LOW LIGHT.  Since 90% of your shooting will be indoors, that's the most critical for real estate.  Basic rule of thumb is:  garbage in, garbage out.  So get the best you can afford (and trust me, the sky is the limit with these things!) and pay most attention to the low light issue.

If you're going to be narrating or walking through the house with on camera talent, you should also pay attention to the audio.  You'll need a good quality microphone.  You really can't use the built in (crummy) one included - you need an external mic.  Sony is notorious for forcing you to buy their proprietary equipment with many of their models (not necessary a bad thing, but they tend to be more expensive and you have fewer choices, obviously).  If you're not going to have on camera talent or will be narrating during post production, it's a non issue.

Also be sure to check about compatibility with your computer.  Those that record on small DVDs are worthless if you're going to be editing.  Plus, on some computers with side loading DVD trays, you can't use them at all.  Even those that record to hard drives aren't the best if you're going to be editing.  I stick with old fashioned TAPE.  Quality is just as good, you can always replace the tape... if you run out of space you just pop another one in.  But check with the compatibility of your camera AND your computer and the editing software you will be using.  All don't necessarily play well together, as usual with computers!

High definition cameras produce beautiful videos - that's what I use.  But be prepared ...   you need some major computing power to process the very large files, and some major storage capacity, as they run about 1.5 GB per minute. (I just purchased my 4th terabyte drive for storage!).