I would hire the absolute best most experienced developer you can. Hire someone with startup experience that can do the hands on work needed now, but also manage and scale the development quickly.

I would say use the title VP of Engineering for the new hire. IF they are a rockstar, then you can promote them to CTO. If not, you could hire a CTO.

I would move yourself into another C-level title such as Chief Product Officer. CTO really means deep experience with tech which you don't have.....and that's ok because you are a founder that kicked ass on the initial version. Now you can bring in the talent to really scale the tech side of the company.