Arne,
The framing is indeed 3/4" thick. I wouldn't pay the price or the weight penalty for 5 quarters wood.
It sounds like your bolts are going thru the sidewall horizontally. That's perfect! 5 bolts that size on each side is plenty!
Sounds like your're getting the hang of it... BTW, you are going to put glue in that joint, right?
Mike...