EBay handles collection and remittance of taxes from an increasing number of states. I combine shipping on won items but please aggregate things and pay in a single payment to save multiple paypal payments.
$1 basic shipping. $20 and under, I use the ebay standard envelope. Over $30, I
use a cardboard mailer where appropriate. Over $50, tracking is required; $5 for domestic. $2 letter shipping for international/$15 for ebay international tracking.