Hello Dave
My husband though much older than you had stage IV base of tongue and a 9cm tumor , a whopper.
We decided not to go the surgery route for just the reasons you are questioning. We were assured that surgery was the second line of defense if needed. As you can see by my tag, it was the right way to go for us.
Absolutely get a second opinion, we did, and it made us fell much better about the decision we made.
You have already found a wealth of info, we are here when you need us.
Take Care
Marica