On weekends it's usually 4-6, on weekends anywhere from 6-12 depending on interest. The ability to post events publicly when people are playing should help alert people when games are going.
Forgot to mention, max playersize for TF2V is 128 players. Peak playercount we ever had simultaneously was 30 or so. Maybe we can reach that number again someday.
According to Steam group, in just over two hours.
Place is a ghost town.