The price is a $1.5 monthly subscription for using Mag Configurator in all platforms.
Your mag should have a public firmware version in order to receive the configuration. By default all Mag have this firmware. If for some reason yours doesn’t have it you can use this instructions for set it: Mag 250 Flashing process or Mag 254 Flashing process
Yes! Just set a rule on your router forwarding the port 22.