In addition to "longest walk possible" are there any good guidelines for finding trails/areas in the southeast that are typically less crowded on holiday such as the 4th? State parks here become overcrowded and very loud on summer holidays.
My answer is not specific for a particular area or a particular date. I like to find trails, areas, that are less crowded in general, and estimate the seasonal pattern mostly on availability. Signs of less popular areas:
Of course, this has the marked disadvantage that it's also harder to find those areas at all. It helps to know the area, to get a good map that includes not only popular trails but also less popular ones, etc. In my area, I've never met another hiker in routes that I designed on my own.