Yes, but check first, actually if you like camping, I really recommend it....
Everywhere is free except campgrounds with facilities. There are hundreds of campsites accessible by car for free. Campgrounds like Mortimer have nice hot showers and a host but you need to $20 per night to stay there
Yes in certain areas. Check for availability with a ranger.
Yes just check in at the pisgah Forest ranger station.
Yes you can in designated camping area's. Try God's Country / Upper creek. If your not, familiar with the area, best bet is to find someone that is before, hand that can show you in person.
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