Advice Starting Business for High Income Earners (I will not promote)

I’m 37 and have had a successful sales career in highly complex enterprise technology within the aerospace sector. I currently work for a large company but I have worked at several small companies, including my last job where I was the first sales person hired and I took it from $7M in revenue to $20M in 24 months, scaling from 8 to 40 employees. I’ve grown my current business from 10M annually to 65M in 6 years. Having worked for both small and large companies and across many industries, I’d consider myself fairly well rounded in experience. That said, I have long considered building a business on the side that would provide a second income stream and also protection (I don’t see many past 50 working in in field), so future proofing my income is the goal. I’m also very oriented towards the service industry that won’t be so easily disrupted by AI (I currently work with AI and I will barf if I hear about another AI startup). I’d want this to grow to something that would afford me true financial independence long term, defined as not having to work and not having to worry. Personally I’ve built up $3M in savings/retirement (I max out everything including a back-door Roth) and my income fluctuates between $400K and $700K per year. I have pretty strong work life balance despite a fair bit of travel (25-50% depending on what’s going on). The reason I bring this up is this is my biggest mental barrier to starting a business is I make really good money now with high quality of life. Looking at dumping another 500-750 hours into a business that might do $250K in revenue at 20% net margin is hard math for me to swallow. But I’m no stranger to 60-80 hour work weeks either. When I look at the numbers of certain businesses, the revenue output is far less per hour compared to what I’m doing today. I understand it could/would grow, but effectively I’d be sacrificing quality of life while simultaneously lowering my output. This is perhaps the most important metric I’m measuring as it relates to this decision: output. In 24 months I would need to be producing more output (dollars per hour) than I am right now. On the low end I’m at $260 per hour now. For those reasons above, picking a business/industry and pulling the trigger has been difficult. I need something I can scale part time, where the constraints that would govern the business are things I could mostly handle, and ideally the capital to start is relatively low. While I’ve considered buying businesses as well, I look at debt service and a PG as a possible non-starter that puts at risk my current income and assets. So in short: I have a strong W-2 job I plan to keep, a sales background, and capital to invest, but I won't risk my retirement savings. I want a scalable business that can eventually run without me and be possibly sold. I would love anyone’s advice or insight as to how to proceed. Questions burning in my head: Industry and opportunity\ Given my situation, what business would you start or buy today? What overlooked industries are boring but highly profitable? Where would a strong salesperson have an unfair advantage? What industry would you tell me to avoid, and why? Buy vs. Start\ 5. In my position, would you buy or start, and why? 6. Which path gets to stable cash flow fastest with the least owner time? 7. What makes an acquisition a good turnaround versus a trap? 8. Which path builds more value toward a large exit? Running it alongside a job\ 9. Has anyone successfully run a business while keeping a demanding job? What made it work? 10. When did you know it was time to hire someone to run it, and what did that cost? Money and downside 11. How do you structure a business so a failure can't touch personal assets? 12. How much capital and time did it take you to reach break-even? Blind spots and hindsight\ 13. What do people with great jobs consistently underestimate about starting a business? 14. What would you do differently if you were starting today? 15. What am I not thinking about? 16. Who else should I be talking to?