what are the legalities and stuff of doing it yourself.
Not sure what you mean by that, exactly. There are lots of tips in the forum about setting up a business structure, if that's what you mean.
Taxes are just like any other income (even with cafepress, you have to pay taxes on the income earned once you make over a certain amount).
You just report what you earned to the IRS and when you have a business, you can write off some things that are related to running your business (like the cost of advertising, web hosting, etc).