In our current project we have four different TFS2010 Team Projects in the same Team Project Collection. The reason for this is that different parts of the project wanted to use different team project templates (CMMI vs Agile).
All projects now use the same template. Therefore we have now reached the conclusion that it would be better to merge the projects into a single team project. This raises several questions:
Thanks for your help!
Unfortunately, TFS 2010 doesn't allow you to merge team projects.
Stucturing Team Projects and Team Project Collections is one of the most important strategy decisions to make before starting to use TFS. Unfortunately, a lot of the customers we help don't make the up-front planning necessary and don't understand some of the limitations in TFS around merging, moving, splitting, etc. team projects before they start diving in to using TFS :(
When we have consulting engagements where customers want to consolidate their team projects, we end up having to do a lot of manual work to migrate the artifacts. We have built some tools to help us with this process for work items but for the most part it's a lot of tedious consulting work. The migration utilities always end up needing to be customized for each customer as well since they usually have different business rules for how they want to migrate.
Ultimately, a "migration" doesn't end up bringing over all of the information and you end up with some other problems like date/time stamps being different from what they were originally. (I have heard it referred to as a time compression issue with migrations.)
Some additional thoughts for each of your original questions:
It's not the best story for you but hopefully it will help your planning out some!