I have attended several games at HVA and I will answer the questions posed about the facilities. The ticket booths are not an issue at HVA. There are three windows at the permanent booth and the line is run efficiently. Also, in addition, there are HVA staff members selling tickets to line members paying with exact change of $6, no wait.
Yes, the visitors bleachers are small. I don't know how many fans travel with Maryville as opposed to South-Doyle, but the Cherokees didn't fill the visitors section last week, so I don't see it being much of an issue. A lot of people watch from the fence area anyways.
The parking is the worst part. There is one entrance/exit to the school, and all of the separate lots feed into that one two-lane street. I've waited over an hour exiting the stadium at Hardin Valley before. (However, I wouldn't worry about being in the area late like one user said. HV is one of the most upscale areas in TN so I think you'll be fine)