I've got one of these coming to me in the next few weeks. Is it possible for me to install with the Home Premium retail ISO, use it for 30 days, and then enter the key from the license that hasn't yet arrived?
Yes, you can. Even if the key is delayed, just rearm to use it for another 30 days in trial. You can do this for a total of 120 days and endlessly using a tool like Timesurfer's IR5.