5 ft. Rain Diverter Aluminium

In my opinion; You may but you might need to put down more flashing above it to cover the gap at the lower end of the run. The diverter is only so big and can only handle a variation in pitch by a few inches in adjustment.

Yes it should. French doors are wider than this one piece is designed to handle. Just add another piece or two until you get just beyond the opposite edge of the door frame area. Keep in mind tho... the longer you make your diverter, the more it's going to show from under the shingles. You may want to get some aluminum "flashing"; cut it to the needed size and put that down under the shingles on the lower side of the diverter area to catch the rain from shingles above it. You'll understand when you start putting it in place over such a wide door.

rusty nails

I would assume you're talking about the "drip edge"... it keeps the rain from running down our facia, eventually ruining your wood.

Yes

The height of this product is 8 inches.

Thanks for your question. This item is only available in select geographic locations and we only sell this item by the box of 10. You can special order this through the store but it will be in the box quantity.

No it can not be bent. It should be installed at an angle for run off.

I can not answer this question as it was not designed for this purpose. Primarily used on asphalt roof allocations.