I have decided what I want to do......

Here where I live registering a business name is done through the courthouse. You fill out paperwork, which includes getting a tax ID number from the IRS and then pay the fees, file the papers and you're good to go.

Do you have an accountant who does your taxes? If so, check with him/her and ask what the best answer is in your state. It will vary from state to state.

I recommend starting an Ebay store. I would not just go buy used books. I would do research on Ebay and see what type of books are selling on there and then look for those types of books at garage sales, thrift stores, etc. Also, you might want to look into finding a wholesaler. Buying on Amazon to sell at flea markets won't make much profit as they shipping costs on Amazong are about $4.00 per book.

I would simply start an Ebay store and then see how it goes. If your store takes off, and you start building up an inventory, then you need to a way to organize your inventory, a storage area to keep the books, and to probably to legally incorporate your business. There are tons of books on how to do this : )