The term "project" is very ambiguous ... if by "project", you mean a group of people working together to produce one or more deliverables, then yes, you would create a team area for each new project.  On the other hand, if you consider each "release" of a product to be a separate project, then you would commonly create a single team area for that product, and schedule each release of the product for a specific iteration in the timeline of that team area.   In other words, focus your team area and category design on your "teams" that are doing the work (the purpose of "categories" is just to automatically route work items to the right team area).   And don't worry about accumulating a lot of team areas or categories ... just archive the ones you don't need anymore.   WRT who should own those streams and components, the primary purpose of ownership is defining access control.   So normally you either assign a stream/component to the project area (if everyone should be able to see/update the stream/component), or assign it to the team area (if only people on the team should be able to see/update the stream/component).