A long time ago, I planned to do a 'snakes on an airship' type rat quest (in homage to the Snakes on an Airplane movie). Then, I realized I didn't have airships in my world and further, that I didn't like ratquests at all. Today, we purposely don't have any introductory ratquests, though we do have dungeons suitable for low-levels (the difficulty of those dungeons is higher than what I think is your intention).
Instead, we have stray dogs, filth rats, chickens, crabs, seagulls, etc.. that players hunt in the alleys and streets of the city. These are neutral creatures that are always wandering around the city and don't normally attack anyone. There is something sublimely satisfying about watching a young hero having to start his/her journey from the ignominious roots of killing crabs in the streets for food and gold, in plain view of everyone, to eventually becoming a powerful champion. Players have actually commented on such as being formative to their concept.
Whatever you choose to do, make it relevant to your world. IMO, the standard ratquest trope is so tired. Not just the rats, but the need to do the quest at all. Look for ways that accomplish the goal of providing introductory challenges in relatively low-risk environments for players, but that don't feel like the activity is only incorporated as a 'rat quest' and has no other value to your world.
