I'm about to self publish my 2nd book. I promote heavily to my small niche market and often buyers find it on Amazon. If I simply use CreateSpace as my printer, a few hundred at at time, do I HAVE to let them have the Amazon sales? Can I set up my own Amazon page and do FBA?
If you choose to use CreateSpace, you have a couple of different options available to you. The first is to do as you asked and buy the copies yourself and then sell them through your own site or in person for events such as book signings. According to their guidelines, you can buy copies through your own account at cost plus shipping and handling. The "Buying Copies" tab includes a calculator that will help you guess at the costs. One of the issues you may want to consider before doing this is the matter of then shipping the book to the eventual buyer. This will be an additional cost to you which will eat into your royalties. Also, you will have to handle the accounting for sales and the reporting of income yourself.
Another option is to use the CreateSpace eStore (see the "Distribution" tab on the same page). This will allow you to set up your own web page for the sale of your book, and Amazon handles all the details like credit card processing and shipping the book to the buyer. It doesn't mention it on this page, but Amazon will also track your sales for the purpose of reporting income, which can be a big help come tax time. With this option, your readers are not "officially" going to Amazon, but Amazon is handling everything on the back end for you.
Either way you do it, Amazon is going to be getting their share. With the second option, however, you save yourself the additional costs of shipping and handling, both from Amazon to you, and then from you to your readers.