I am a former restaurant owner, working long hours like you, and taking home even less. It is a business for a certain type, that is for sure.
From my observations of my own mother, and two friends, I would reccomend against real estate. How about hours like you are putting in now, with no pay and all expenses are your own to cover?
I was fortunate that I had a background in industrial sales, and I am back at that in great position, but that is because I have 25 years of experience.
Not to disagree with the MBA advice, -- I am part of the way there myself, not at a top 25 school though -- I do not think that that is the current reality. Besides that the top schools and lesser ones are very expensive.
What I would reccomend is a trade -- welding, machinist, hvac. plumbing, electrical, etc. You will always be in demand. This is not what I did, but it is what I am helping my oldest son do.