Remove Power Switch
After looking at more details on the Adafruit PowerBoost 500 Charger, I noticed the breakout for the ENable pin. Looks like I don't need the FET power switch after all. The PowerBoost can handle the power switching. Yay!
I've remove the power switch and added an Adafruit Trinket - 3.3V. That will give the project the smarts it needs.
I increased the size of the LiPo battery from 150 mAh to 500 mAh.