The setup has been pretty straightforward so far for me. Our group has about 4 deployed in various places so far. One issue we've run into is the site itself has changed greatly since launch. They switched from thingspeak and google maps API to MapTiler and OpenStreetMap, which ended up shedding some of the key features we used.
This included features like graphs for different averaging times, graphs for different date ranges, real-time r2 values, and displaying the uptime of the sensor. I was assured by the PurpleAir team that these features are being worked on and will be restored at a later date.
Their customer service is pretty responsive, but they do own the site and the data, so I'd recommend watching for changes like that and talking with the team there relatively frequently. Also, on an unrelated note, they just sent out a voluntary recall for the PA-II and PA-IISD charge cables, so make sure your cable wasn't recalled.