No way. Buying a house with at least half your net worth at age 57 is reckless and dangerous.
First off, have you calculated the taxes you will pay on the 401K portion of your assets that you are counting towards your $4 million? If you haven't, you are in grave danger. If $1 million is in your 401K, you don't actually have $1 million. You have $1 million minus the taxes you will pay on this money, so if you just use the dollar value on your account statement you are overcounting.
Secondly, this monstrous home is going to have a super sized property tax bill. Do you even know how much that will be? And, sure, you have solar power, but there are going to be many expenses for such a large house. Taxes and insurance top the list, but there will be many more. Your remaining $2 million, if it is even that, might not be enough to support your lifestyle with this house. As another posted pointed out, that's about $80k a year. The average property tax rate in Tennessee, per Google, is .56%. That means just your property tax bill is going to be nearly $12,000 a year or 15% of your safe draw rate from your investments, if as I pointed out your 401K value is calculated correctly at it's after tax value. Homeowner's insurance will probably be at least $750 a month. (I used MoneyGeek website for estimates but they only went up to $1 million and the $1million amount given by Statefarm was $588 a month.)
Third, do you even know how much, in the end, this money pit will cost to build? Is it actually $2 million? Will there be costs overruns? And when it is done, will it even hold it's value, let alone grow in value.
I could go on with more reasons. But I won't. Suffice it to say, you need to get out of this situation now, while you can. Buy a smaller place. Let your investments grow and compound.
Buying a house for half your net worth at this stage of your life is a terrible idea.