The thing to aim for is to schedule your breaks so they don’t occur at the beginning or end of your job. In a three hour period you can take two short breaks between the hours or you can take three short breaks (one out of each hour) and rotate the timing of them backwards so you don’t break at the end. For example, when playing 7pm to 10pm, you could break at 7:50, 8:40 and 9:30 (or 9:20 so the last break isn’t too close to the end).
I usually keep my breaks to 10 minutes. If there are speeches or toasts during the dinner, you may find your breaks being set for you.
I never eat on the job. That’s just my personal rule. My breaks are too short and I might spill on my clothes or get food on my teeth which would look very unprofessional. I try to eat before leaving the house, but when that’s not possible because of timing, I take liquid dinner in a can (Slim-rite if you don’t want too many calories, Boost if you’re underweight) and can drink that with a straw during a break or in the car before unloading the harp or after the job. It’s enough to keep the hunger pains away.
I probably would not repeat any selections unless requested, but if necessary, repeat the pieces from the very beginning. Chances are many people will have missed hearing them the first time or have forgotten what they heard earlier. They’re listening subliminally. It’s just background music.