A mixolydian piece? Probably the hardest thing to do is to write good modal music. The easiest thing to do is write a mediocre modal piece. It's hard enough for beginners to rely on 'ionian' and the minor scale for decent harmonic drive and variation-yet remain coherent and interesting. I should now as that's the situation I'm currently in myself. I would hold off on learning the ins and outs of Palestrinian 16th century modal counterpoint. It's all well and good to throw in modal stuff like a phrygian half cadence until then. Focus on mastering common practice harmony, there's a reason this chord wants to resolve in that manner.