Oh my goodness, I have had sooo much trouble with my scar from a 4th Degree. It hurts during sex at times, and sometimes bleeds after sex. I had my first episiotomy with my first baby. It was horrible! I got an infection from it, even from the salt baths and using the blow drier to keep everything dry. I was very sick with it. Now I have scar tissue there, I can feel it when I run a finger over the area. I had 3 more kids after my first, and every time I need a few stitches, which adds to more scarring :( Oh well things we do for our babies :). I have been trying an oil to try and keep the scar tissue supple. I hope it works.
I had a 4th degree tear and episiotomy with my oldest (10lbs), 3rd degree and episiotomy with second (8.6lbs), and 4th degree and episiotomy with the third (10lbs)...... they dont sew your vagina completly shut (it just kinda looks like that for awhile, until all the swelling and redness goes away) they stitch tog the skin from anus up to vagina and then and then around your vagina leaving what looks like a very small hole. I found a website with a little more details..
check it out
http://thewelltimedperiod.blogspot.com/2005/05/episiotomy-and-husband-stitch.html
As far as the stretch marks dont really have alot of those but from my expierence I havnt found anything to get rid of them....
good luck, and congrats on the baby!