These would work with sheet metal as well
No. Self drilling screws make holes only large enough to accommodate them. if you want larger holes to deal with expansion, drill these separately.
This type of thread is especially designed for soft materials. Assuming your pergola is aluminum extrusion, a self tapping metal screw would be best. Don't forget the rubber washer - very important.
Don't drill in the valleys of your fiberglass roofing panels and use screws with a rubber washer to seal the hole. I used that on my fiberglass roof - and no leaks in some heavy rains and also snow.
I believe that it is 3/16, and a hex driver bit is included with each package of screws.
You should have a set of bits; such sets are not expensive. For fastening to wood, use a bit which is slightly smaller than the diameter of the bolt to the bottom of the threads. For fastening to metal, use a bit which is slightly larger.
I have not seen any such. But the 2 inch screws are long enough to hold four sheets of polycarbonate (at corners) and the beige spacer on typical wood stringers (2x4 or larger).
Yes I used them for my greenhouse. You have to pre drill the holes for them , however,. They work well
You may find the correct recommendation at the website of the manufacturer of the panels. Variables include factors such as the amount of wind in your area.