Subdirectories AND Subdomains - IA help needed

Hi everyone. First post here. So far WPMU has been an amazing resource to learn Multisite! Hoping one day I can contribute, but for now, I am a newbie in need of some guidance. I have a client that has three levels in their website hierarchy. Each level of the hierarchy will consist of a different theme structure, but within the same design. Let me explain further. There is ONE corporate site. This site will be heavy on information. The second level will have THREE branch sites, with more to come. This level will also contain a lot of information regarding each branch, as well as certain forms and information submitted, by users, and pushed to each branches respective email address. The third level, contains employee websites - at least SIX, probably more - branching from each of the Branch/second level sites. These sites also must be able to collect information submitted and distributed to the employee's email. I have included a mockup to help further display. So each level - 1-3 - will have restricted access, controlled by the person in charge of that level, to change and/or create content. (I know this is the point of MS so I'm sure none of that needs much attention?)

My question is, how should I structure this site? My original thought was to use both subdomains and subdirectories, e.g. This address would obviously be the third level within the site - the employee's website. I think this is possible through the multi-network plugin ( but I am not sure if this is 1. needed and 2. the smartest way to accomplish my mission.

I appreciate the help in advance!