If you can get the customers to pay before get a CTO, you can give him 10-20% and a good salary. If not, at least 50% and you will have a hard time convincing someone good enough to help you achieve success.
I think this overstates the value of the MVP. It sounds like the CTO contributed only technical assets, while the OP is the one building the actual business.
That's what I was thinking. I won't be able to afford a "good salary" for a while, and it's still part-time only. I was thinking ~15% and then salary once we're there.