Hi moretolearn,
1) To enter the item specifics for an item, please use the "Choose Item Specifics" link that appears directly under the category field after you have selected a category that entails item specifics.
2) Auctiva Shipping Insurance policies will cover USPS shipments but, if you would like to purchase your insurance through USPS, you will want to disable the Auctiva Shipping Insurance setting in your account.
3) You can specify that immediate payment is required by checking the box next to that option in the checkout settings section of the lister page.
I hope this helps=) If you would like further assistance, I recommend filing a support request using the appropriate link on our help page:
http://www.auctiva.com/free_auction_software_help/help.aspx-Mike