Go the people mover! Fortunately for us, we had upgraded to a people mover when the gremlins arrived, so the car dilemma wasn't a big deal.
I'm glad to hear your hubby has come round, it sure took mine a few days (or if I'm completely honest, months!). Like you, baby #4 wasn't on the cards, we had decided we would have another, but we were planning for a few years down the track when we got a big surprise.
I guess what helped was taking the "what will be will be" approach, after all, you can't really change the situation (barring termination of course, which was never an option for us, and sounds like you are the same), so you might as well get on with it.
I found being pregnant with two toddlers and a preschooler much harder than having a newborn plus the rest, mostly coz I have awful pregnancies, but honestly, once she was out, she's just slotted in and goes where we go etc. She is a funny little thing, she literally flew into the world a hundred miles an hour and hasn't stopped since, she tackles everything head on,which may be a result of being the youngest of 4 - she has to fight to make herself heard. She is pretty feisty too, doesn't let the others boss her around much.
Best of luck over the coming months, you will be fine, and hubby will get better with the idea as time goes on - looking at Willie with lil miss these days it's hard to believe he didn't want her at all to start with, they have a really special bond.
If you need any help with practical stuff, let me know