Get copies of all the paperwork now, take screenshots of the business accounts in case you are suddenly blocked. Lock your stuff down now, personal email access, sole bank account etc, if you can print stuff, print it and leave it with a friend or at your Mum's. If you don't have a sole account set one up now. Lots can be done online.
Most men, most, will not leave to suddenly be solely responsible for all their own cooking, cleaning, ironing, food shopping, organising etc there is usually a stupid woman telling him they can be better than his wife and look after him.
All the time he was filling up his pension pot whilst you were a sahm is half yours because you are married you are entitled to monies you did not earn. Everything gets put into one pot, house, cars, pensions, savings, investments etc and 50/50 is a starting point although they do take into account your ability to earn and provide a home for you and your child. Usually it will go more toward you if you are a the lower earner.
See a solicitor, do not take his word for what he can and will provide in this. Most offer 30 minutes free consultations. As above, he has been planning this but probably won't have through through the day to day stuff. If he wants 50/50 is he going to be able to do the school runs on his days? Will he have to sort wrap around care? Are there any spaces in the wrap around care place? Every 6-7 weeks his child has school holidays has he factored in the cost of childcare on the days he will have her? It isn't up to you to have her or sort out or pay for his days. Of course you will open your arms to have your DD but don't let him think that, don't let him think for one second you will just sort everything out for him.
The stuff he has never had to think about are now his to think about including life admin for her like haircuts, uniform, shoe shopping, dentist appointments etc. They all cannot be your responsibility. Maybe pointing this out might help him see clearly.