You sound really sensible, which is so refreshing to hear.
My main advice would be to just tread carefully.
I am massively stereotyping but many millionaires have narcissistic tendencies.
Many successful men would not choose to go with an ‘unsuccessful’ woman, unless they could benefit them in other ways (be a live in housekeeper type role).
The fact that you admit you are a broke, single parent and then he wanted you to work in his business has made my alarm bells go off massively.
I think you are being very sensible by having a ‘way out’ if you ever need to.
You will be pretty well off when you are living together though.
You have your own place which you will be renting out, which should pay the mortgage.
You’ll be working FT and only paying half of the bills and for your DC, which leaves you with plenty and I would take say 20% of this each month and put it into a savings account so if you broke up you could rent somewhere until you can get your home back.
As with any unmarried couple, I believe the best way to do things is have separate accounts and then a joint account for shared bills and expenses.
E.g 50% each.
So both of you would put in 50% of your wages.
For you it may only be £10k a year and for him it may be £50k+ a year but all joint expenses like bills should be taken from the joint account.
The other 50% is for you to both do what you want with it, whether that’s spending it all or saving it and in your position I would try and save as much as you can.