I stayed at this campground 5 or 6 times lots of tent campers and I’ve never seen it more than half full great place

The whole campground is free but it's also first come first serve. So you could get there are not find a space. I haven't experienced that but I've also never been there in summer time.

Yes for up to 14 days.

So far as I know it would be possible, just not sure it would be advisable. You might want to check the average temperature and humidity for that area for the time you are looking at going.