Without knowing anything about this particular area; I would like to add my personal opinion.
I guess your market is House Brokers. So do you have anyone in the industry that you could ask questions: "How do you add a house to your website today; what do you like and what don't you like?"
The sidebar approach is probably the way to go here though.
"Big property / small properly" all depends on what area you are talking about.
One hectare might be big in New York City but considered smaller in other parts of the world.
But this is just nit-picking.
These properties would be better in an "Dimensions" category in the sidebar and doesn't really relate to the name of the property.
Why a sidebar vs one page layout?
Because in my experience some housing brokers put up the ad in advance with just names, dimensions and locations. Later they add proper images, inspection protocol's etc.
A sidebar is easier to just add the basic information quickly and add additional information later. Rather than having to scroll through pages of information you're not going to fill in either.
Also a one-page layout would require the broker to actually read through all the information first in order to know what he / she can add.