I recommend you to read this: Troubleshooting QlikView Server in a virtual environment 11/13 . For your questions:
Yes, you need to install QlikView Server on both machines in order to cluster then.
You need to open ports (4747) for the QVS services to be reachable. Only one of them should have the QlikView Management Console installed. Make sure they have the same amount of resources, and make sure they are dedicated - we do not recommend memory ballooning in any way.
Windows Server 2012 is supported - recommendation is to use the latest version of QlikView, which is v11.20 SR7.