Simone has kindly answered all the questions that I had within a few minutes and with clarity.
The instructions for the self check-in were clear.
The apartment is located very close to the train station of San Pietro (< 5min walk) which you can use to reach different parts of the city. You can also take the bus from there, or even simply walk to Piazza San Pietro (~5-10 min) or the historical center (~20 min).
The apartment itself fits the description well. It is comfortable, nicely decorated and has basically all you need to function.
There is a supermarket at ~5 min by walking.
I recommend this location which is a great base to explore the city.