I second Michael Barnathan on 2 points and from my past experiences.
1) When you are building an MVP, alpha or beta versions, you will be quite open or realistic about the timelines and it often happens that once you see that there is some traction, the team tries to set unrealistic goals and the job of developer/CTO becomes very tough.
2) I do believe that working out a contract with the CTO is a really good option, because with a new CTO/developer the overhead(3 or 6 months based on the product/service platform) will be quite significant.
3) While you contract the current CTO, you can ask him as a part of contract to train a group of interns/devs about the platform and stack. If contracting is not an option, then definitely hire an experienced lead/Senior dev and put a bunch of interns to work and train under him. I do agree with you on not hiring a CTO directly, there are own set of problems which come along with it.
4) As far as hiring a Node.js developer, be open to a developer who has experience using multiple platforms and in the long run if there needs to be a change in the stack or a need arises to use a different framework, the developer can handle the transition smoothly.