I really liked the atmosphere you built with track 8! The tension around the opening bit with the text message leading into some unique sound design was so cool, especially after listening to music with a happier feel to it!
With regards to your mixing and mastering, composing with headphones is exactly what you were supposed to do! While you're mixing the tracks, it's important to make sure you watch the levels, which I believe is the little meter at the top center of your screen (I use Ableton personally so my levels are in a different spot), that way you know your songs are mixed well even if the headphone volume might be lower!