The goal of this paper is to suggest that the creation of a manual for language

The goal of this paper is to suggest that the creation of a manual for language teachers Is a good idea for a doctoral research.
So I would like to find answers based on bibliography to:
1. How to choose a topic for your doctoral research?
2. How to start a manual for teachers and how to start research and practice?
Suggest ways to start
3. Is it something that will be useful for foreign language teachers?