As long as Inter-VLAN Routing is disabled the VLANs will have no access to each other. Configure the router and connect to the guest network. Then try to reach a device on the corporate LAN and you will see that you are blocked. Enable Inter-VLAN routing and test again. You should now be able to access corporate resources. Remember to disable it and test before going live.
As an additional precaution, enable Wireless Isolation within SSID to block guests from accessing each other. They will have access only to the internet in this case.