I'm too much of a power noob to give any proper advice (in fact that's why I decided to get a coach to help with the analysis), so I'll limit myself to two comments. You may want to check out the racer's forum, good thread in there for people new to power, some of it get a bit technical but overall a good read. As for what I do on my Garmin, my main screen shows 3 second power, %FTP, total ascent, ride time, and power zone. Once I had my FTP established (using the 20 min test but have not retested in some time), I put a chart of all my zones on my top tube so that I can remind myself where to be based on my workout. As an example today I rode with a decent warm up then 5 min at 105% FTP followed by 5 min at 85% repeat and rinse for 30 minutes followed by warm down. I don't even have speed on my main screen anymore although I do on other ones. I've enjoyed tailoring workouts to power and feel like it's helped me a fair bit.