can shaco carry

100% Yes.

Practice makes perfect, maybe try visiting shaco subreddit, the payout is not as good as with other jglers though if i'm going to be honest .

If he snowballs, yes. Otherwise, he would be deadweight; no dueling potential, minimal teamplay, etc.

Shaco is a really good durring his powerspikes but he tends to fall off if the enemy has comunication. Honestly you can carry him especiall in low rlo when people dont k ow what they are doing but with the low teamfight potential he has and only his abilty to work if you have game knowledge and know what to do when you would probably be better off playing someone else untill you get a basic understanding of the game because shaco is not a forgiving champion. One mistake and you basically a worthless champ making the game feel more like a 4v5

YES. Counter-jungle, gank often early to get kills or at least summoner spells to help your laners farm, and prioritize drag/rift. Shaco's clone makes it easy to collect objectives quickly all over the map. Kills are important to snowball, but if the enemy team is skiddish / wards really well then you NEED to focus objectives.

yes, but there is a 99% chance that you playing as him cannot, as you are in iron.

low elo yes, high elo no