1. I would buy a powermeter over Chinese wheels
2. I recommend getting a proper computer over using your phone
3. If you are dead set on using your phone, use the wahoo fitness app. The metrics provided are the same as their head units
4. If I were to do it over, I would get dual Assioma pedals. If you are going to go with a crank, stages or 4iiii are great (I myself use stages). Second thing on crank based power meters, there is an issue with shimano style right side with respect to calculating power, so going left side (non drive side) is what I would recommend.

Computers:

For what you are doing you can't go wrong with Wahoo or Garmin.....However, I just got a Stages Dash M50 and am blown away with the visual metrics it provides. The Dash will be replacing my Wahoo on my main bike.