No closer than 10 feet
When you do parallel parking you must align the wheels strictly parallel to the curb, and then shut the engine off.
18 inches
Your vehicle should be no more than 18 inches from the curb.
12 or less inches
yes
Ideally you should be as close as possible to the curb when you finish parking, just to lessen the chances that your car won't accidentally get hit or scraped by cars driving too close to you on the side of the road. However, 12-18 inches is usually a safe distance away from the curb.
From the Calfornia DMV web page on parking: When you park alongside a curb on a level street, the front and back wheels must be parallel and within 18 inches of the curb. Park parallel to the street if there is no curb.
12 inches from the curb
12 inches from the curb
I think that would depend on the county and country in question. In the UK, "next to is next to" and you get a ticket.
1 ft. (30cm.)
18 inches