In the lobby, by the elevators. Offices generally don’t rely on walk-in traffic the way that retail or food/drink do.

The biggest challenge I see is in how to segregate commercial and residential traffic. Residents will not mostly want to live somewhere that they encounter random strangers walking through their hallways all the time. A purpose-built residential tower can limit access per floor fairly easily. In low-rise buildings with living area above retail, you segregate at the door to the upper floors.