To answer your main question; you can't be slow and be a winger as the winger are expected to the be the fastest guys in the team in order to carry the ball in the try zone without being tackled. if you are not that slow and you have a good sidestep and a good footwork you might play at center position, if your kicking game is good you can be a full back... as for you friend he might try flanker, qed: Steffon Armitage
If you've got good hands, fly half is a good option, with plenty of opportunity to use that footwork
No a winger needs to be fast.
Yes. I've played with and against some not so fast wingers. What they lack in pace they make up for it with their defence, their positional play or their ability to read a game.
not really
no chance. that is forward speed, not back speed.