Your success as CTO is mostly determined by yourself. Understand what's required of you. Start interviewing other CTOs at other startups and understand what their roles are and what they need to do. Build relationships with them so that you have a network of advisors if you ever need someone to have a chat with. Learn a lot. Do a lot of research. Do a lot of thinking.
Leadership is not all about experience. Leadership is also about listening. And all leaders start from somewhere. Once you have an open mind to learn, you'll realize that being a leader is about being courageous and responsible for the happiness of other people. It's also about helping to steer the ship in the right direction. But with all startups, you're making decisions on minimal information. What you need is a mind of learning. Test and learn and never assume you know it all. Then you'll be fine.
The salary issue is another big issue. Would it be worth to trade away your salary for the experience that you get? How will you survive? Do you have enough savings? Do you have a backup plan? If you're not getting any salary, then you should get significant amount of equity. And at this stage, as the CTO, will you also have to build the product? Job titles at early stage don't matter much.
Lastly, do you trust your boss enough that he will steer the ship correctly? Do you think he has what it takes to make it all work? And how is your relationship with him? Will he listen to your opinions or is he going to make all the decisions by himself?
Good luck