Ok- I'm an ebay freak, so maybe I can be of some help! I do have experience in buying and selling.
In your listings, be sure to mention that you take paypal as payment only. It would be to your benefit though to accept money order because not everyone has a paypal account. This way everyone will have a payment method available to them. I know that with credit card transactions through paypal there is a fee to the buyer, I don't know about the seller, I've never accepted a credit card payment.
I personally don't like the postage calculator unless you have purchased a scale that will determine the weight and the cost of the shipping using various shipping methods.... next day, air, parcel post, etc. Insurance is available for the buyer. Just be sure to get the accurate fee or you will find yourself paying for insurance.
You can visit
www.usps.com and you can sign up to receive FREE the flat rate shipping boxes. I LOVE THESE! They come "broke down" and are very convenient, as you can use them to store your item while waiting for it to be purchased. The USPS will ship these to you at no charge for the boxes nor shipping, and regardless of the weight, you can ship in these boxes for the flat rate. Just be sure though that the boxes does not bulge at all because they will not accept it. Also, and I'm sure you know this, you will want to be sure to charge the buyer for shipping. Some people try to profit from shipping, and I think this is very wrong and not moral. Please do not do this.
If you have an ebay store, please be sure to tell me about it. Give me your seller ID. I buy alot from personal sellers, but try to stick with ebay store or power sellers. Good luck and I hope you are successful!