Most NFL players wear a jockstrap, and some wear a cup
Majority of NFL players wear oakley visors.
NFL Players wear cups. As a former NFL player, I got out of the league in 2007 and now play Arena ball, you would be crazy not to wear a cup. There are some teams that don't (I think the Eagles for the most part don't) but 90% of other players wear cups.
You can. NFL players can wear any glove they want but they have to have an NfL shield on it.
No, they don't have to wear mouthpiece.
They certainly do.
for a custom nfl jersey
Approximately 40% of the NFL players don't wear them according to this article. http://sports.espn.go.com/nfl/news/story?id=2314899
what NFL player wears #60