Base miles are primarily for those looking for performance lasting more than 2-3 hours. There's tons of recent research that shows this and you should go read up. Long and slow is the first thing you chuck out of your training book if you're on a limited time schedule as it's very little bang for your buck if training for criteriums. Why waste more than half your training time going Z1 or Z2 when you only have 10 hours a week to train? You shouldn't, as you don't need the endurance for 2-3 hour events.

Most areas within the US you'll likely only see criteriums. I wouldn't even be concerned with road racing until you sign up with a team (you'll likely pair up with a criterium team anyway if you become serious about it). Since you have 20+ hours a week to train you'll be putting in some base miles but it's more important for you to find some nice group rides for you not only to learn pack riding skills but to build some comradery and help keep you motivated to keeping up. There's plenty of generic training programs available on the net if you enjoy structure but with 20+ hours a week there's plenty of time to just ride for the fun of it and work in some specific intensity workouts.