You will need 20% down for the house to avoid PMI insurance. If you can't do a 20% downpayment, you can't afford the house.
After putting 20% down, your loan will be 2,800,000. Taking advantage of today's low interest rates, if you have great credit, you might be able to get a 3% 30-year fixed mortgage. That comes to ~11,805 per month or ~141,700 per year for the mortgage alone. You also have to figure in property taxes, which could easily be anywhere from 30-50k per year... So really, the house will cost you 180,000 or so a year with property tax.
Since you will be in the upper tax bracket because you are "ultra rich" according to the government, about 40-50% of your income will be taken through taxes. Assuming you can keep 65% of your income, you will make about 360K/year. After your 180k/year house payment including property tax, you will be left with 180k to live on.
If you can afford this, you might want to think about putting off buying the home until you have around 50% to put down. If you take 2.8M out for 30 years, you will pay an extra 1.45M in interest on that 3% loan. If you can put down 50%, you can do a 15 year loan and will get a better interest rate. If you could get a 2.8% interest rate for 15 years on 1.75M, you would end up paying around 180K a year like before, but will only be paying ~410K in interest over the duration of the loan.
Another thing you might want to think about in affording a house like this is how much money you actually make... meaning, if you are thinking of being a surgeon or something, factoring in high malpractice premiums to how much money you make, etc. Just something extra to think about.
I hope this helped :)