I think that anywhere in the 3x range is good. 4x is way too high in my opinion @____@
I think 35 might be a good level. You get the milk quest soon afterwards, so it gives you a chance to explore.
I'm also still wishing for the party pass thing xD Like Omie said, if it's a friend that needs to be plvled or a cleric that just wants to duo with a higher leveled friend a party pass can be pretty beneficial.