You sound a little bit naïve, @Cratie. You enjoy your independent, autonomous lifestyle now but you will NOT have that with children. Even if your fiancé performed a 180° turn, going part-time with work, getting stuck in with the laundry and childcare, doing night feeds and nursery pickups, your life would change radically.
He isn't going to do that - because workaholics do not suddenly become homebodies, and because his solution to the load-sharing question is for you to work part-time in his business! Surely you can picture how that would work out?
What you could do: Carry on much as at present, but with twice the outgoings for a nanny, laundry and cleaning services. You'd also carry a far bigger mental/emotional load, as you'd be doing the planning, fire-fighting and managing children's social business on top of your job, relationship and personal life.
Or become a full-time SAHM, and it would be full time as the big man's out earning his big money, or a part-time one with a mish-mash of competing responsibilities and still no personal life.
I'd say you need hard talks but neither of you have a realistic idea of what's involved. You actually need these hard talks with extra people present; people who won't sugar-coat the reality of life "in the trenches" with young children.
Plus, as others have mentioned, you cannot assume perfect health and no additional needs in either your children or your husband. This is true at any age. In your situation, the probabilities of less-able children and a physically challenged husband are quite a lot higher.
Don't float into this thinking everything will work out fine. Use your rational brain. And, I agree, listen to your instincts: they're telling you something.