Since no other position is really viable (right now), I'll delve into jungle AD Shaco:
To answer your first question:
Only if the other team isn't extremely tanky, or have more than two champions with hard CC.
Also, be weary of your ELO situation. At low ELO, an enemy team may not grab a pink ward of oracle's to combat you, but I promise that in higher ELO they will.
To answer your second question:
I think AD Shaco is perfectly fine as-is. They buffed his E a few patches ago, and that was nice. Other than that, I think his balance is great. He just takes a high skill curve with which to be competitive.
To answer your third question:
I honestly haven't played any ranked yet this season due to my failing internet connection that randomly disconnects and won't reconnect. Last season, at almost 2K ELO, I didn't see many Shaco's, and, the ones that I did happen upon, were decimated. Shaco has been around for a while, just like many of the higher-end ELO players, so most experienced people know how to shut him down at this point.
To me, Shaco is a waste unless you have practiced him time and time again. If you get early ganks and early kills to feed him, you have a chance; but if not, he's a dead champ on a team mostly because he won't have the CS farm on which to fall back.
I don't mean to discourage you, but if you want to play Shaco in a decent ELO, you must practice him often. THERE WILL BE EXCEPTIONS TO THIS RULE. I know some people can play him very well without much practice, but that is a select few compared to how many people try- trust me.