Length will vary from 1" to 1-3/4" for various thicknesses of drywall and application types.
You can use drywall nails or drywall screws. I prefer the screws.
You can use drywall nails (ridged) or drywall screws. I am not a drywaller, but have done lots of it and prefer the screws.
Commonly #6 gauge.
About 4 grams.
20
Metal drywall screws are usually fit with a small plastic pre-grooved sheath which taps the screw into the drywall and wooden beam behind it. This results in a clean and secure penetration of the wood for each screw.
The most commonly used are #6.
No, they are adequate for many uses.
Yes, that is exactly their purpose.
They evolved in the 1970's .
I use about 28-30 for that.
Coarse 1and 1/4 drywall screws are best.