Above the belt line. Definitely.
Which side doesn't matter. It doesn't hurt it to sleep on it. Mine is in the right. I sleep on it no problem.
They will mark your belly with a permanent marker where you want it. It's what they did with me. Request it. Then they know where to put it when you get in there.
Just ask to make the stoma long. If possible. I realize it's not in all cases. But definitely bring up the length of your stoma. I did and she gave me one that is 3/4 inch long and works well at that length.