I'm not sure on the requirements, but unless you are using the dev branch there isn't a proper dedicated server system yet, so chances are total players will be lower. See if you can find out TigerWolfs specs as he has hosted a fair few Arma 3 evenings and they ran fairly smoothly. Other option is to just host a public server and keep an eye on it to see what performance is like while mowing the lawn or something.