Advice on potential multi-user site

I've been asked to pitch for a site and I'm wondering if WPMU is the right way to approach it, or if there is a better solution. If nobody minds, I'd like to outline the site requirements below and solicit some opinions?

The site will be available to Party A Clients and Party B Clients. Tiered membership is sold to Party A, who will register and add their information to the site for Party B to see. Tier 1 is basic information, Tier 2 allows them to post more information and come second in site search results, and Tier 3 allows them to post even more information, come first in site search results *and* have access to a database about Party B clients.

Party B clients can browse the site for Party A information (with differing levels of search results, as mentioned above), and also opt to add themselves to a database that Tier 3 Party A clients will have access to.

I guess this sounds kind of like a dating site (it isn't)! But it is about connecting the right kinds of people. Is WPMU the way to go with this?

Thanks in advance.