Last month I had to navigate four flights of steps when returning to our very nice apt near the Pantheon - not a deal-breaker, but not fun after a day of intensive Roman walking. If you're near a Metro stop in San Giovanni, that would make access to other areas of the city easier.
One day I walked from our second apt in Trastevere to Mercato Testaccio - you are away from the touristic center, and there appeared to be an issue with one of the trams, so it did feel a bit isolated. But it depends on the experience you are looking for - you would eat better in Testaccio, and mingle with more locals. But no major tourist sites outside your door.