Hello! I'd say the expression is "so on and so forth", but yes! It just adds emphasis to the sentence (and yes, it's also the same as etcetera!). I think "and so on" is a little bit more informal than the others, but they're basically used in the same way :)

Yes, but so and so forth is more formal. I hope this helps :)

Yes

Is the same as "et cetera"?