Three years of a long commutes behind me - 96 mile round trip to begin with, down to 70 miles after a few months.
I cycled quite a few one way trips on the 96 miler (ie 48 mile ride to work) and a couple of round trips. Used to sit there wondering when it was naptime and eating constantly!
70 mile round trip got a bit more manageable - cycled round trip once or twice a week throughout british summertime.
Things that will make life easier:
Military-like levels of planning. Take as much as you can in the day before (food, clothes etc) to limit what you have to carry on the bike. However this means if, say, you want to cycle in Wedneday you have to be organised enough to pack all that stuff up on Monday night, to carry it in with you on Tuesday...oh and then bring it all back again on Thursday!
Good facilities at work. I was lucky enough to have a nice shower, somewhere to hang cycling stuff to dry, and kept my bike in the office so had no qualms riding my nice (and therefore fast) road bike in.
An understanding partner to feed you when get in - you will have little time or energy to do anything much apart from eat and sleep on days you have done the round trip! For 80 miles you are looking at 4-5 hours of riding, on top of your working day.
As others have said, you are starting at the hardest time of year! Hardly ever used to manage it in the winter. That far in the dark was depressing and also pretty dangerous on the roads I was using (a lot of unlit fast A road).
EDIT: 4 mile potter down a cycle path to work for me these days