Two things come to mind: You are making too many changes at once, and you are pushing yourself too hard too soon.
Take baby steps...a couple miles one day, and gradually increase your mileage. Don't change bikes or bike parts until you've ridden about a hundred miles so you get an idea of what you would like to change.
I can relate to the excitement and drooling over all those other expensive bikes. The bike shops have to mop up after I browse them. Try not to look at them while in the bike shop. Remember, a $1500 MTB is not necessarily much better than a $500 MTB.
As for your diet, I suggest you keep your diet the same until you get used to the bike, then gradually reduce what you don't want to eat or drink. Go to your nearest bookstore and pick up a book on bicycle training, they are very helpful and encouraging.
Sounds like you have a LOT of willpower and motivation, which is a very good and rare thing. Dive into bicycling too fast and you will burn out fast.
Give yourself a few weeks to get used to everything, and it will become a fun thing to do. As for hills...yeah, they are a chore, you might want to find other areas to ride and alternate.
Hang in there and keep us posted!!!!