Need Advice… Complicated Blog/Site

I am trying to put together a multi-part website/blog/forum.

I chose WordPress for maximum flexibility in blogging. Here’s the main functionality I am trying to put together using plugins.

Main Page (non-blog): Traffic cop allowing visitors to go to areas they have access to (sub site 1, 2, 3).

Sub Site 1: Pages, events, shopping, landing pages for google, blog open to general public.

Sub Site 2: Pages, events, forums, shopping, blog only available to ALL registered users.

Sub Site 3: Pages, events, forums, shopping, blog only available to a subset of registered users.

I would like for a single user signup to control access to selected pages, shopping cart, forums (by category), blog posts (by category).

I’ve downloaded about a dozen plugins after reading them carefully but its just not “gelling” yet. I am looking at zen-cart but am uncertain about the integration.

As you can see, I need a LOT of help/advice.