All of the things that need to be covered in setting up a group buy?

So, I'm being encouraged by a forum veteran here to setup a block erupter group buy on another bitcoin related site. Doing things like that makes me stupid-nervous. I don't like money, I don't like handling money, and especially dealing with _other_ peoples money. However, it might actually be worth doing and seeing as I've never taken on anything like this I believe it would be a worthwhile experience just so I can learn (obviously I'm also looking to purchase block erupters, but there's a benefit to me (and others) here making them cheaper at the cost of my time).

So, typically what goes into doing a group buy? I'll try to write down my thought process so far:

Create a new bitcoin address for input BTC.
Collect required amount for group buy, along with address, etc.
Order block erupters
Have users paypal the shipping amount?
Ship block erupters?

What are things I have to look out for? Best to keep all the data in a spreadsheet with receiving addresses so when asked, those people can sign via that address to prove they are who they are? What am I missing?

Edit: Say I don't get enough backers for the group buy? How do I deal with refunding, and the btc that will be taken out as a transaction fee?