I've managed a quick service restaurant and I can tell you this is the stuff of dreams for someone trying to manage that staff, Your estimate of the staffing costs is way too low. Hands down the biggest challenge was turnover. It took us about two weeks to train and employee and about a month after that for them to be really good in the kitchen (if they were ever going to be). The day crew were stoners and slackers, the night crew was high school kids. In other words, no one cared much about the job. Our turnover rate was probably 90% in a year and we offered a pretty nice food service job compared to something like fast food. (It was a McAlister's Deli. On par with a Panera.) Anyway, not having to train part-time staff, deal with their ongoing drama, substance abuse, constant scheduling conflicts, etc... would be worth a lot.