Coach Bomber, I'm looking forward to my second year next year so I can relate.
If you have Underwoods book you have the foundation. EVERYTHING else is based on the type of players you will have next year. In HS FB you go with who ya got. Study your players as much as the book. Pick your formations and plays accordingly. Don't worry about quantity of plays. Watch your players run the same play repeatedly. There is always some kind of varience that they bring into the play.
You will end up running the plays that work so scrap the old one's as you go to keep that playbook manageable. Don't neglect the special teams. IMHO 6-man workouts don't need to be so position oriented because of how players play so many different positions. Whatever you can do to get the guys into their best shape will work.
In a short period of time I've observed many good coaches and I haven't seen any magic wands yet. What I have seen is basic football. Some of it is done better mechanically that's all.
THE MOST NEGLECTED AREA for new coaches is in their relationships with their student-athletes. Put just as much effort into this as you do everything else. You are there for them not the other way around. Examine why you want to be a teacher. Do your best and your personal brand of success will find you.