I've been told its all about routine, and that the first 6 months is the hardest! But after that it's pretty smooth sailing most of the time!
You only get give what you can cope with, and if you get stuck don't be scared to ask for a break or some help!
I'm due in December, and my youngest will be 12 months old and we also have a 8 year old. So I have asked the same question many many times. I'm sure you'll be fine