ISTM a lot will depend on what classification(s) you plan for your portal.

As for the format, I would seriously consider the wiki model for a few reasons:

1. As an established, standardized tool, almost everyone understands it. One of my biggest complaints about DoD "portals" of all kinds is that they are all different and many are poorly designed and confusing to navigate. A known standard interface and simplicity should be a priority.

2. Allows for collaboration among all your stakeholders.