I think the key C5 concept to understand when doing sites like this is that everything revolves around PAGES. For example, instead of creating a separate database table for your properties, you could create a "Real Estate Property" page type, and then your users just add a page of that type to represent a new property in the system. This page will have the editable areas for users to enter content, but you probably also want to create some custom attributes for meta-data on each property (for info you can filter on when listing properties in other places). You could also group the property pages into categories by simply adding them under different top-level pages of your site (like "Residential", "Commercial", etc.).
To list out properties, use the Page List block and create a custom template for it (search the forums for all of this stuff -- there are tons of resources about it).

Depending on the complexity of your application, though, this may not be appropriate -- if there's LOTS of data to be entered or if there is complicated logic involved in the data, you may wish to create a dedicated admin interface for this so it's easier for users to enter data than it would be using page attributes. If this is the case, then Mnkras is correct that doing everything yourself with the database is possible (C5 stays much more out of your way than most CMS's if you want it to) -- you just create your own tables and some models, controllers, and single_page (views) to interact with and display that data (seehttp://www.concrete5.org/documentation/developers/pages/mvc-approac... for more details on how to do this approach).
Do note, however, that C5 only does about half the CRUD for you -- there is an ActiveRecord implementation in ADODB which you can use for your data models, and there are helper functions for outputting form html, but other than that you need to code up this for yourself (validation, processing, etc.)

Hope that helps.

-Jordan