Copy all posts to main site or read posts from child sites?

Hello!

Basically, I’m working for build a Real Estate Agencies net, where the main site named imobilix that will provide the technology. But, to increase my profits I want get internet access to the main site through the offers published on child sites.

So, my questions are two:

1 – What approach is better, copy all posts and updates from child sites to main site or just read posts from child sites?

2 – What’s the best solution provided by WPMU to put fire on the road? :wink:

Thanks!