There is a very good discussion of staging available on this website, along with some excellent personal observations by Brian Hill.
I would encourage you to check it out at the following link.

http://www.oralcancerfoundation.org/facts/stages_cancer.htm

It looks like your father has a difficult road ahead, and it's great that you are advocating for him. It's a very difficult road, but one that many here have traveled. Be sure to stay in touch and get your questions answered.
As you have no doubt seen it said many times before on this board, treatment at a Comprehensive Cancer Center is strongly encouraged. The link I gave you also includes a link to the 50 best hospitals articles.

It's really tough to even speculate what to expect in the coming months. As you have said, his other health issues may determine what type of therapy will be offered. His doctors will be in a much better position to make those recommendations following the biopsies on Tuesday.
In the mean time, browse the website, educate yourself, and write down the questions you want to ask his doctors. Keep a notebook. It will prove invaluable.

Come here often with your questions.

Good Health,

Chuck