Wow, you will have your hands full, won't you? I knew a woman on another board who was a SMC of a 2 year old, and then did IVF after a number of unsuccessful IUIs with DS and got pg with twin boys. She was only planning on one, and was fairly freaked out at first. The babes are around a year old now, and she's doing just great! Busy, but great.
Congratulations on your pregnancy! It's bound to be tough at first, but I'm sure you'll get into a routine, and it will be very worth it. I don't have any more specific advice, but I know you'll be fine.
Deborah