What are the key topics or areas that you must have a vision for once
you pitch your prototype to an investor, or assist the CEO in
In my experience none of this "overall system architecture, technical roadmap, how to scale the system towards a certain market goal in the next 3 years, how the technical architecture will serve and empower the business need" matters, directly, to investors. They might care about some of the details when you get to the point of nailing down terms - but they are details.
What investors care about:
Where is the prototype?
How is the prototype performing in the market you're trying to address?
How are you going to grow that market over what time scales?
Why do you need our money and how are you going to spend it wisely?
To get investment you have to have convincing answers to those questions. Some aspects of those answers will likely be within your domain of knowledge. What those answers will need to be depend on your business - so it's hard to give generic lists of things that will be of concern.
I'd strongly recommend trying to meet and network with people working at companies at as similar stage to where you are now - and companies who are a few months on from where you are now. Talking to people about how the investment process went / is going. If at all possible meet with investors before you are asking for investment. Find mentors.
A lot of the stuff I read about CTO roles online is just plain wrong, or company specific. If you go talk with several companies, and several investors, you'll begin to see that people's idea of what a "good" CTO is changes quite a bit between organisations.
To some extent investors will not care if you are the right CTO for the company in three years time. They care if you're the best person to get from now to 18-24 months from now where you are actually showing some traction and growth. After that - they can always "encourage" you to take another role ;-)