To answer how much information is needed to begin a formal project it is important to outline what information is needed. You sort of answered this in your question, enough preliminary details to plan or propose. These preliminary details (most already explained in previous posts) would include . . .

1. Description of the project. What will the device do?

2. Why is such a device needed? What is its market niche? What does it offer to the consumer? Perform a competitive analysis and reflect on any market constraints.

3. Management plan and design approach. How/why are you qualified to undertake such a project? What technical skills do you need to hire? Any technological restraints? Consider legal, safety, and environmental realities. Even a general schedule of completion; milestones.

Once these details have been satisfied, the project development phase could begin. This opinion is formulated from my experiences working on Capstone as an undergraduate.