You have asked some very specific legal questions best answered by a lawyer, and you should NEVER take legal advice from nameless/faceless folks on the internet.
And I am no lawyer, so what I am about to say should not be construed as legal advice of any sort.
That said, it varies from state to state. You will need to deal with taxes and licenses on a state by state basis, and you very definitely need to know the requirements for each state you visit. I will tell you now that the tax boys have NO sense of humor and would as leave throw you in jail as spit. What's more, if they catch you in violation, they tend to make a wild guess as to how much business you could possibly have done in the state, and then assess you a tax burden based solely on that. And pile penalties and interest on top of it. If you don't pay up, you will go to jail.
And before anybody crabs about "the Obama Administration," be aware that this has nothing whatever to do with the feds, it is strictly state law, and it has been this way ever since I started in business in the 1970s and no doubt long before that.
