If you are planning on selling a lot of items online, I would invest in a small digital scale: Portable Electronic Digital Kitchen Food Scale 5kg 11LB | eBay
. It will save you money in the long run by always getting the correct weight of your package and not say...over guessing it and over paying. Plus it will allow you to print out your own shipping labels online using paypal knowing that you have the correct weight of your package without going to the post office and back to get your package weighed. They only charge $0.19 for delivery confirmation as opposed to the post office's rate of $0.70, which adds up after awhile.
Plus when you print your own shipping labels at home you can just hand your package over to your postal worker when they bring your mail to you, saving you trips to the post office which I know everyone's favorite thing to do is to wait in line.
I would start saving everything you think would be a "nice sized shipping box", all you have to do is take the box apart ~ turn it inside out ~ tape it back up ~ and bam ~ you have a free shipping box! I also make sure that the box is wide & long enough to hold a shipping label.
The little styrofoam peanuts and bubble wrap are the lightest of packing materials, you'll find that newspaper really weighs things down. Whenever I get a package in the mail I carefully remove the label and tape on the box so I can re-use it and of course, re-use the packing material.
You can send it First Class only if your package weighs 13oz or less. That will save you the most money. If your package weighs more than that, sometimes a priority flat rate box is the way to go and other times Parcel Post is. You can always calculate the difference here: Postage Price Calculator
When you print your own shipping labels, the bar code on the label will help get your package shipped in almost the same time frame as Priority Mail for a lot less. That's what I've been told at the post office and that's what I've experienced as well. I have great reviews on eBay and on here for fast shipping and I've always used First Class.
As for accepting money through paypal, just pm your buyer with your email address associated with your paypal account and they will send money to that address. Just remember that paypal will always take their cut :O)
Hope that helps