Cadence definitely the right place to start, since it shouldn’t break the bank.
I’d do some research on cadence if you haven’t already — you mentioned getting up hills in a higher gear to be faster while also keeping HR down. That’s definitely an option, but it can come at the expense of your legs (and worst case, knees).
Conventional wisdom today (as I understand) is that if you thrash your cardio, it’ll recover fast; thrash your legs, they’ll recover more slowly. So there tends to be a bias towards higher cadence (80-100rpm or so) for performance, with lower cadence useful for strength training.
Good luck! Cycling is a wonderful sport. Focus on the numbers and gadgets if you like, but at the end of the day remember to have fun :)
My recollection is that the DVD included that library, but it’s been a while…