Very quickly.
First, read the book Getting Things Done by David Allen and make an informed decision.
Second, your system seems to rely on predetermined priorities organized into quadrants. This type of priority assignment, strictly speaking, is not part of GTD. However, priority is part of the Four-Criteria model used in GTD to choose which tasks to complete in the moment.
Third, contexts are used as the first factor to limit one's choice of what task can be completed in the moment. They can be a person, place, or thing (nouns?); pretty much anything. I have not found reason for multiple contexts or tags to be useful in GTD, but other workflows might apply value to this type of element differently.
The factors of the Four-Criteria model are:
- Contexts
- Time available
- Energy available
- Priority
Fourth, read the book. If you are considering moving away from your current productivity implementation to GTD — understand the tenets of the methodology by reading the book and not by requesting another's interpretation.
Good luck.