Lets look at this from Google and a PageRankô perspective. If the root domain is sitting at PR3/PR4, adding 40,000 pages is going to suck the life right out of that site.
I would definitely throttle back the release of new pages. I'd really focus on click paths and "core content" first. Get the upper level click paths indexed first and then once you have some PR to work with, release more.
The problem I see as others have noted is that you are basically regurgitating the same content that millions of other agents are using. Those pages have little to no value unless of course they have been set up differently than everyone else has done it. ;)
Competing in the Real Estate sector in itself is a major task. I'd have to imagine that it is one of the most heavily filtered set of SERPs.
What will probably happen (if you release 40,000 pages at once) is those new pages will get indexed and many will end up in the Supplemental index shortly thereafter. Then you'll have an unnaturally high ratio of pages in the Supplemental index which in turn may have an effect on the overall performance of those pages not in Supplemental.