The master election process is handled automatically, so you don't need to configure a "master" AP as such. So in the first instance just plug 1 IAP in and configure this accordingly, set the Virtual Controller IP on this AP. Once the first AP is configured you can plug in the second AP, the second AP will automatically located the first AP (elected master) in the broadcast domain and download the configuration.
When configuring the IAP, do you not even need to find the IP from your DHCP server, look for the broadcasting SSID and connect to this, it will either be "instant" or "setmeup" depending on the software version.
To configure the Virtual Controller IP address, access the GUI and go to System > General > Virtual Controller IP