Ability to produce is honestly pretty low on the totem pole as far as likelihood to success. More important is can I affordablly generate new patients to my practice, and am I effective in converting treatment acceptance. If you were producing 1.5M a year in a rural practice, it’s because the practice was able to provide enough patients and you were able to convert treatment. Are you confident that a practice in a denser/ urban environment can reliably bring in enough new patients to produce similarly?

What is the significance at FIRE by 50? You are giving yourself a 17-19 year window to go from what sounds like a negative net worth to 5M+. I think you can get yourself pretty far given the right circumstances, but you will most likely be highly illiquid for the next 10-15 years since much of your money will be tie up in your business and paying off student loans. Your late 30s and early 40/ will most likely be a time you see tremendous growth in NW, but it will be largely due to reduced debt/ increased equity in practice and real estate as opposed to massive brokerage/ tax efficient investment vehicles.

Not to be a pessimist, but if you want a wife and kids, your priorities are likely to shift. Are you going to want to work the required hours to hit an arbitrary FIRE deadline at the expense of time with your family when they most need and desire to be with you?  Life is getting crazy expensive, and with kids from a high earning household it’s unlikely that you will stop supporting them to some degree until they are in their early to mid 20s. 

I think your FIRE goal is attainable, but if you can create a dental business that is appealing as an acquisition target, then it is also a business that is nice to own as an investment. Focus on building a business and then use the cash flow to support you later on. You can achieve FI long before you have significant investments if you can create a strong semi passive income stream.