It is normal to feel sore in a lot of places for a week or two when you just begin to ride.
I recommend that you don't make many changes to your bike until the initial soreness has had a chance to subside and your your body has had a chance to adapt to the new odd positions you are asking of it. When you do make changes to your bike, do just one little change at a time and then ride for a week or two to see if it really makes a difference. Your body is going to be changing and making new muscles to suit your needs.

12 hilly miles is pretty big for a first ride- don't expect too much from yourself at first. Work your strength up gradually, and don't let anyone push you too hard if you are not ready to do more. Above all, ride safe.
It's good that you have an experienced rider helping you.
Congratulations!