1. It is assumes that you are always using run/walk intervals.
2. The short "tempo" runs are whatever pace you decide. Usually, you should be working at whatever your next important race is, but that is up to you. Long run pace is your race pace + 2 minutes per mile. And keep in the mind that that is a speed limit - i.e. you shouldn't be going any faster than that - and not a necessarily a pace suggestion. On long runs, you can certainly go slower (or even walk the whole thing) and get the same benefit.
The one concept that I had trouble with (and I don't think I'm alone on this) is that you are looking to hit certain paces. The interval suggestions are simply suggestions that work
for most people. Your body may be different so you can try different intervals and see what works best. Can you change your intervals for different paces? Yes. Can you stay with the same intervals to get different paces? Yes. Again, it's what works best for you. I know that Chris Twiggs (running coach and head of the Galloway customized training program) has a video somewhere (maybe
YouTube?) that he shot of himself running at three different paces - one a minute slower than race pace, one at race pace, and one a minute faster than race pace - all using the same intervals to demonstrate this concept.