Multiple WP sites from same DATA TABLES (not just DB)

Greetings.

I would like to power two (or more, perhaps) different WordPress sites from the same data. Note that I am not looking to drive multiple sites from the same database in which each site has it’s own tables in a common database.

Rather, I want these two sites (or more) to use the same data (same posts, pages, etc), without having to copy/paste the data between multiple blogs. So, these sites will actually hit the exact same tables when they respond to end user requests.

The idea, for those who may be curious, is to have multiple presentations/formats of the same data. I’ll use my current project to demonstrate:

1. Primary site is the main place the author will post to (hopefully, the only place). This site will have a fairly traditional blog look. This site will contain a very wide array of topics (actually sub-topics, as they are all related).
2. Secondary site will have a less bloggy theme and will show a very small subset of posts/pages/etc from the primary site. Most likely, the secondary site will not show any comments, though it may report the number of comments that have been posted to the post on the primary site.
3. I’d like the process of “copying” posts between the sites to be as automatic as possible – So repeated customizations to RSS embeds and similar hacks will not work. Ideally, the author can mark posts that are to appear on both sites with a custom field (or category) that the secondary site theme will check for.
4. The purpose of the secondary site is to serve as a teaser marketing piece, while the primary site is the meaty destination.

My questions:

1. Is this safe to do?
2. If “no”, why not?
3. If “yes”, what is the best approach?
4. Also if “yes”, is there a safe maximum number of sites to deploy in this fashion?

Apologies for the lack of links – These sites only exist on my dev box for now…

TIA!
Gilad