You can attach the roof panels directly on to the OSB if you want, but most roofers will place a moisture barrier down first. Also, I found that if you install insulation on top of the tar paper, and then place your roof panels on top of that, you can eliminate most of the noise created by storms.
The 1-1/2" Woodscrew is a #9.
Should be fine. I'm guessing you are putting metal roofing over asphalt shingles. If it is normal construction with either a plywood or OSB sheet under the shingles should be good to go.
This would not be suitable for that use. First, you don't want a gasketed screw. There is no need for a gasket in your application. Second, you want a flat head screw which will drive flush with the surface of the OSB. These would stick up and interfere with the roof paper and shingles. You say a shed, but I am assuming not a flat roof. You need a 3 in 1 pitch minimum for shingles. BTW, the screws in your picture are for attaching metal roofing.
If you want to secure something say 1/2 - 3/4 inch thick on the roof, .............
It really depends on your job and budget.
Yes, but sometimes you have to go through the manufacturer to acquire them.