Tamino database design philosopy

My company is purchasing Tamino so I am playing with the starter kit and thinking about design issues. I am wondering what is the thinking of current developers/users about the use of collections and doctypes. Our first use will be the aggregation of information from many sources that is not already in XML form. The main purpose is to impose common metadata and facilitate searching. Since everything is being converted to XML for the first time we have the possibility of using a single basic schema for all documents. The total will be a couple of million documents.

What is your thinking about one collection and one doctype vs. one collection and many doctypes?