Hi OP
You had a plan when you got pregnant to share childcare. Now he us changing it. You're a partnership he can't just decide on his own and leave you to like it or lump it. The children are legally and morally a shared responsibility, is he really going to turn round to them when they are older and explain that he never looked after them when they were sick as he earned a lot of money you see.
My husband earns double what I earn. We changed our hours so that he gets in a little late snd I leave a little early so we can manage pick up and drop off. It's a pain as we both don't get enough hours at work and often work when kids are in bed as well. We both try ans do a day from home when meetings allow, which helps. This is becoming more and more common now, I've seen a big change towards this in the last few years. We share days off when the kids are sick though in reality it often ends up me doing a bit more as he's often away.
Also I work 4 days and got a promotion on my return from mat leave -
In your case your husband didn't need the promotion - if he hadn't taken it and you'd gone back to work then the family finances would have coped. So he did it for himself as much as the family. You need to be a bit selfish as well.
The options are
Talk to him again and try and make him take some responsibility. He can not sign away his responsibilities to his children. You never agreed to take on responsibility for them 100pc. You may as well be a single parent! You will find resentment building and may cause issues in the future if this carries on. You will probably find at weekends and holidays when he should be giving you a break, he won't, as he will find more work to do as he gets more senior, or it'll be easier for you to sort the kids as he doesn't know their routine etc. In which case you will find you're better a single parent as at least you'd get every other weekend off. Try and get him to commit to something, leaving on time a couple of days a week or working from home one day
Do what he wants til the kids are older and reassess (I've never heard something as patronising as starting a little business though!)
Find a part time or flexible role with a view to keeping up with the industry and reviewing hours when the children are a bit older and accepting it won't be the career you want for now but may lead to it eventually
Work and get a nanny or childminder or nursery ans au pair etc. Dont worry if you don't quite break even, it's his responsibility to pay for it since he's the one refusing to do any practical childcare. Lots of working parents have the same issues and they manage. Yes it will be tough however you would be taking this option to help with your career long term.
Personally I'd be doing the last option as I would like to protect myself long term and he is being v unreasonable. I'd also want to show my kids that fathers don't get to make all the decisions and expect the mothers to fall in line and that looking after the children is everyone's responsibility