I'm interested to know what your lives were like when you met.
When you started talking about the future, living together, children, did you say what your wanted and he agreed? Obviously he told you that he wanted to be a gentleman farmer, and you agreed, but was this right at the beginning?
Because, as far as I can tell, neither of your has checked in with each other over the years, to listen, and see if it's still working.
Did he know that you were aiming for private schools, holidays, ponies? Did you grow up with those things and assume this was a basic level of expectation?
Did he do something different when your meet, and you agreed to continue with the career, promotions etc without stopping to say "I can't keep doing this, at this level"? Not when the first child was born, or after the next?
He may take 3 days off a year, but you do know that it's possible to plan ahead even if it's a long way ahead, and have others hold a farm together for a week or 2 over the years? Has he got to a point where he can't imagine spending that much time with you or the children?
Has he maybe discovered that he finds "people" difficult, and actually finds a solitary life on the farm far easier to deal with.
If he could pay the rent 10 months out of 12, what made you feel that you had to keep working to the point of breaking all those years? Most people would be happy with that, if you're both working.
If we were talking about a mortgage, and he was able to cover 75% of it, and then your job could cover the other part, plus utilities, food, presents, etc...
If you all went away for one long weekend a year, and then you took the kids away a couple of times (to family, camping, something low key), how much would you have needed to earn?
Because if you've sold a business that covers land, school fees, you only need a small mortgage now... how easy would your life be right now if you had continued to rent the place you have now, and just had a small rental property, or put some in a pension etc etc.?
I think your husband has kept quiet in a desperate hope that things would just stay the same, despite the blindingly obvious that your bar has been raised and raised, or I should say changed.
Your expectations aren't necessarily better, but they take you away from where you both started. That's fine. But obviously he just wants to keep doing what he's doing, whatever the cost to you. And you wanted, and got, a f ton out of earning so much, but now it's too much and you're barrelling on in a different direction. Only this time he's really panicking.
It's a mess.
The only answer might be to leave, but you need to acknowledge that your did all these things that you thought were important, and now you're here.
Oh, and you should know, your children would probably still be a credit to you, even if they hadn't gone to private school, or had ponies.
If the answer is that you need to sit down and talk, otherwise you're splitting up, then I hope you would both make time and space to do that. In a way that SO finds possible. If he is scared or finds it difficult to articulate his thoughts, you may need to be creative. I def recognise a lot of this from my DH, loathes confrontation, but creates confrontation by not saying what he wanted up front.
I think you may need to reconsider some of your goals too.
You very excited to tell everyone about the house, of course, it's aspirational, it's fabulous, it represents so much.
But if you genuinely want it to work with your partner, maybe you need to practise saying "oh, we've decided to leave it for a while, we've got some new ideas, and just want a bit of space to mull over a different plan". That's not embarrassing.
Good luck OP, it's a good job you're capable of being tough, you've got a way to go before your can call this sorted.