I suspect what you want is more complex than any simple consumer router can provide.
The router itself has no ability to control or identify individual users. The guest wireless is just second password for your router each user does not have their own. The limitation on bandwidth are by ip address not users and the pool of ips are the same both for the regular network and guest. You would have to do something like manually assign all the employee ip and let the guest use DHCP.
I also suspect you mean a 200 megaBYTE cap not and a 200mBIT data rate. Many internet connections are not 200mbit/sec so you would need a very fast internet connection behind your router.
The device you want is generically call a captive portal...