Yes. We just showed up at the visitors desk and asked when the next tour was. We were directed to wait in the rotunda until our docent came along. I believe the tours started about every hour and a half or so.

My understanding is that you are correct. They do guided tours for groups but they don't say how large a group is. To be honest I don't think a tour is really necessary. The city of Raleigh was not on the map when the War for Independance was fought and the Civil War never touched it. There are a number of statues and plaques around and in the building so, going and walking the area on your own is, in my opinion, a better option than taking a tour, anyway.