One site to rule them all, one site to bind them…

I’m new to all things WordPress, but I’m interested in making a HUGE website for the London 2012 Olympics. The site will have a wide variety of different areas and, therefore, types for pages (e.g., sections for choosing hotels, for specific sports, for London sites, for buying Olympic merchandise, etc.) I seems to me that the easiest way for me to create my site is to create or use a custom theme for each of these areas. (This will be under one domain name — e.g., all under a singe core url such as http://www.myolympicfolly.com).. I understand the general principle of creating internal links (ala Wikipedia) to get the link juice flowing to the core pages. However, I’m concerned that the approach I’m describing might be perceived as problematic by search engines in that they might think that I’m trying to game the system. Are there any problems with what I’m describing? Is there a better way? (Has this question already been answered a zillion times and I’m just too clueless to be able to find it?) Any guidance will be greatly appreciated!

~John