the "Talk" at 5???

We are expecting number 4 in a little less than three months. My five year old keeps asking all these questions I am not sure I am ready to answer. I learned all the details at 9 yrs of age, but isn't five a bit early? The other day my husband and I took Duncan out for lunch after his doctors appt. He asked how the baby got into my tummy, who put it there (and I tried "God put it there" that didn't work LOL ). He also asked where the baby pottied while it was in my tummy and how the baby ate, etc. Then he asked how the baby gets out of my tummy. I told him as much as I thought I could. The truth I mean. I didn't try to skirt the issue or fill his head with things like "The stork" I told him that the doctor will help the baby out of my tummy. That there is a little.. hallway type place in mommy's body that is called the birth canal and that the baby goes down that little "Hallway" To get out. ( I did not tell him where though.. exactly) I told him that I did not have the same type of wee-wee that he did, that girls are different and God made us so that we can have babies and boys can't. I tried to explain the bag of waters (which was fun, let me tell ya.. Our waitress was doing her best not to crack up) I told him it was a little like a baloon and that there was water in there and a cord that fed the baby and when the baby needed to go potty she/he did so in the water, and when the baby was born the water would go away. Did I do right? Should I have handled this differently? Is there a .. book or something that is appropriate for a five year old that I could read to him???
I am so lost here. I did not expect these questions til later, and I don't want him thinking I won't answer questions when he has them. We have always taught them they could come to us no matter what with whatever questions they might have.
Help!!

Thank you ladies, and Lenora I will look those over

Thank you Dr. and thenk Nicole. THis is not the easiest subject to talk to him about so young.