After having thought about it for a while I think that my idea not to create a separate TOM system independent of MOSS was a bit of a silly idea. The whole point of the system is to exist in any environment, so the first version will exist separate of SharePoint. The main advantage of this will be debugging and testing....
The first version will use simple web pages as stubs to the SharePoint bits, but the final version will need to run in MOSS.
This project will give me an idea of how complicated it will be to produce SharePoint features and how much time will be spent in bug fixing...