I keep articles from Parenting Magazines and fliers from the Dr's office in a binder so it is easy to refer to. I pulled it out and this is what it says on SIDS, "some mothers worry if their baby rolls over in their sleep, but once the baby can roll over, the risk of SIDS is REDUCED. The greatest risk is between 2-4 months." I have a 7 mo old son that started turning himself over when I would lay him down on his back and has been sleeping on his tummy this last month and he sleeps much better doing so.
I praise you for being such a loving and caring mommy, but I would not worry about him turning over on his tummy at night and I would definitely not get up 50 times at night to turn him back over on his back. If he is really upset when flipped over to his tummy at night then that would give reason to go in a help him out. You can help him practice during the day with flipping back to his back. It took my boy a week or two to finally figure it out so the time is coming close, hang in there.
My son also likes to occassionally move himself around and he ends up across the width of the crib like your little one. I just let him sleep that way and figure that if he is that uncomfortable sleeping that way that he can move himself into a new position. As for your little one still learning to move around, I would let him sleep the way he positioned himself unless he starts to cry. He will let you know when he is uncomfortable.
As for the bumper pad, both of my kids never had a bumper and they never had any crib rail injuries. If you are that concerned about it I would suggest getting the mesh type bumper that way you will not have to worry about him smothering and suffocating with the traditional bumper and you also would not have to worry about his limbs getting hurt.
The less worrying you have the less stressed you will be and the more you will be able to relax and enjoy your new role as a mommy. Lack of sleep has been one of the hardest things for me. I notice a big difference in my mood and energy with the amount of sleep that I get so I try take naps while the kids are napping.
Sounds like a mother group would be a good outlet for you to find a balance. This is something I should look into as well since finding that balance the past 3 yrs has always had it's ups and downs. It takes a few months to get a routine especially with your 1st child. Eventually you will find a balance with your new identity. It will come, give it time. Good luck with everything. You're doing great! J. (31 yr old Stay at Home Mom of 2 & a babysitter in NE Portland)