Advice on big family

In my ex marriage I had my son which he is 3 next month. My boyfriend and I are expecting a baby girl in august, he has 2 boys ages 5 and 3. I’ve been so used to being a momma of 1 for almost 2 years. It’s been a crazy transition going from 1 child to 3 and now going on 4 kids. Has anyone gone through this? My boyfriend is an amazing father and partner and I know he will help without a doubt. The boys are such good kids and I love them all so much, but I’m just worried I’ll get overwhelmed. Maybe I’m worrying for no reason since I have no idea how all this will turn out, but any advice is welcomed.