Sharing data from some sites into a portal

Hello there,

I need a help for a project.
I will create a multisite installation for create sites to my clients. The clients sites will be in subdirectories from my mainsite (ex: http://www.mainsite.com/client1/, http://www.mainsite.com/client2/, http://www.mainsite.com/client2/, etc

All the clients sites will be create from the same wp theme (with some changes each one from the CSS styles). This sites will be real estate listings, always with the same parameters (number of rooms, area, price, location, etc).

I want, if is possible (its a service i want to offer), that all information that the clients insert in their sites, be replicate in real time to a Portal.

This image can help to understand:
https://docs.google.com/drawings/d/1zPMqN1HBlXyL1cIbOPWrYPpbRNe_eHaw4pVsyjq8ATA/edit?usp=sharing

Other questions is about managing the plugin’s, themes and WP updates. Any time that are a update there are some tool or plugin that i can use to update automatically in all the client sites? I read some place that exist a tool that create a subdirectorie, install the WordPress with the theme all in the some dashboard.

Waiting for your help
Best regrads from Portugal
paulo