Emily,
Well its a pretty impressive start with your list, good show already. Air cadets is the way to go, get in there, you will get flying time with them.
You will get alot of advice pretty soon on this forum! All I will add is, presently the industry is very low but expect some kind of recovery by 1st to 2nd quarter of next year but I reckon you know that. Not going to affect you though, as you are years away, so your timing is good.
Yes, another back up is a very good idea, just say, you lose your medical, its not over though, as plenty of work to be had in ground instruction in various forms, so perhaps plan B with an eye also on that, so as to stay in aviation. Once you get in aviation and start flying, generally nothing else will do.
Non of the study is rocket science just volume of study. If you have such a passion for aviation you will enjoy it immensely, like myself. Select flight schools very carefully and don't hand money over first, this forum will point you in the right direct regarding that. Ground school, I would personally recommend Bristol Ground School and the forum will probably say the same. Lastly, network, clubs are a good start, a lot of airline guys tend to hang around them on their time off, as they like to talk about themselves and what they do!
Most of all, enjoy the journey, nothing else like it.
PlainTalk