Hi John,
Welcome to the forum. I am sorry you have need to be here, but I am sure that everyone here will try their best to support you through the ordeal.
Did the doctors mention anything about whether the cancer is
HPV positive? You are at the beginning of an arduous journey so it is good to hear that you are a very competitive family and are prepared to fight.
You will probably get your Dad's treatment plan from the doctors soon which will tell you whether he will have surgery, chemo and/or radiation. In the meantime, keep up your Dad's spirit by serving him all his favorite food as once treatment begins, he may suffer loss of taste or may develop difficulty eating. For now, don't worry about putting on weight as it is probably helpful to put on a few pounds prior to treatment.
I am sure Christine B will be along soon to talk about nutrition and hydration. It will help for you to read some of the threads on the forum carefully. That was how I picked up all kinds of tips and had some of my questions answered when my husband was getting treatment. It is important, too, to read the main pages of the website as they contain really important information.
Keeping you and your family in my thoughts.