again, my experiences are on the outdated side, but they're right, getting a business license is pretty easy. it cost me about $25 around five years ago.
uhm, there is a giant pain in the ass when you do this, though, and that's taxes. not only did i have to file a monthly business income report, but i sat through several tedious free classes offered by the post office and a tax attorney, even the small business administration (which was a bust, but they turned me on to the tax seminar). they were all free. i say that because i'm assuming you'll be taking in mail orders, too.
you got your business name and logo, that's a good start. getting the license isn't like getting a liquor license, it's much easier. i am, however, unaware of any resolution in the interstate/county tax controversy. my wife is suffering through that right now selling pampered chef.
good advice with the post office box. a medium size one is all you need, if even that.
doing your own book is incredibly exciting, but it's also a ton of work. once it's barely known you're doing this, you'll get swamped in junk mail, heh heh. it's all fun, though... except the tax seminar. gawd, that bit ass. i suggest calling the SBA and at least ask about free seminars. if you're going to do mail orders, call the post office. note: you'll have to call a main post office, a branch won't do.
hope that helps.