How large can the return box be? Is this location staffed, in case I need help? Are return labels scanned so that I may get a receipt indicating that I delivered the returned item to the shipping location, similar to a receipt from a UPS store?

There arw employeees there to take your big box. Its like their warehouse to received returns. There are bags yiu can put your stuffs in if u dont have boxes. Life is much easier and saving the planet

Yes, there is usually a person at the desk unless they are helping someone else. There is some packaging material (including bubble wrap) and tape available for repackaging. You can print and attach your label there using the kiosk and deposit in the self-service slot or hand to their employee if it's big... if it's big, I'd also recommend original packaging.

This is completely self service. On one occasion I did see an Amazon employee but not sure if customer focused. You will get a email when you drop off.

Yes this location is staffed. You can ask the staff, but i assume you can get a receipt, and you can bring very large packages in.