It really depends on the way you build it more than a specific count per section.
On mine I used M8 bolt, 4 per side on the frame rail section.
You can definitely use smaller bolts, but M8 had the flange size I wanted to see there for counter sinking purposes.

 

Ahhh makes sense, so I should basically just get the weld nuts based on the thread pitch of that bolts.

 

to deal with your exhaust being lower than your frame rails, get a custom one made up. or have a shop weld the hangers higher. I'm pretty sure most aftermarket exhausts out there don't hang lower than the frame rails.

 

Ahhhh that would make sense, the only thing is I would have to have my exhaust re-done also since the hole in my diffuser is already a pretty tight fit for the exhaust.