I can't imagine there is a big scalping scene just based on where it's located. I'd say keep an eye on ebay, craigslist and stubhub. Schedules are usually released a week or two in advance. Based on the schedules from last year artists play from about 11am-8pm .
It is all general admission and from what i've read at least at the main stage they have a GA pit that they clear out after every performance and let the people in line for the next artist enter. I think a lot of the crowd brings lawn chairs and set them up at the main stage and just sit there for the day. So if theres one specific artist at the main stage you want to get close for I do believe its easy.