Hi beadchicka!
I use 22 or 24 gauge to make ear wires. The 20 gauge, while more firm, I think is bigger than standard ear piercings.
I buy my sterling wire from a local shop that doesn't charge a silver surcharge. But, you can get it at firemountaingems.com also, and they have all assortable pricing breaks.
Hope that helps!
Starr