All that you've determined there is heartrate zones. I found this test to be really only useful on an indoor trainer. Outdoors we have too many hills and I would be all over the map with my heartrate. But I could watch the monitor on my trainer and dial in my heartrate at just the right spot. I've since moved on to training by power, which is much better for gauging performance and improvement.
I assume SA means San Antonio, so you have more flat stretches. Heart rate monitoring can be somewhat useful. Set a target of ~ 90% max HR and ride as long as you can there. Repeat as often as you are able and you should see the time at that effort increase. Mix in some high intensity intervals, ride lots and you should be good to go.
As I progress and get more fit and re-test am I looking for my avg hr and max hr to go down with each re-test?
As you progress your power should go up but I wouldn't expect your HR to go down. If anything it will gradually increase as you strenthen your legs which allows you to put more stress on your cardio system. The main result you are looking for is to increase your average power during the 8min test. If you can't measure power directly do the test on a hill and time it.