What the heck. Your advice to a new CTO is to start a small business on the side? I would immediately fire them if I were on the board and they did that.
Why? As long as it is not competition to your employer, your off time is your time. How would it be different from a hobby? And as mentioned, the intent is not to make enough money that you leave your current job. You're still a loyal employee doing an honest full-time job there.