I would also recommend getting more than one professional opinion. My experience was that everybody gave a different answer, and nobody really knew *for sure* - but then this was a few years ago and they may be more educated on it now. Calling the state about sales tax, for example, I got a different answer every time I spoke with a different person.
At the time I had an offline local business established, services for which I was already charging sales tax, and was inquiring about sales & services I was adding that were conducted online and out of state. In the end, it was agreed that I only had to charge sales tax on those sales & services that were conducted with a resident of my state... which made sense to me, but I had received conflicting information from other sources.
We already had a business license at that time, but when we split the business and I began working from home (and online) full-time, I inquired about obtaining a new business license... My CPA said it wasnt necessary as I wasnt conducting business out of my home (ie no traffic, signs, etc) - but I was told by other sources that I "should" (not that I had to, or needed to, it was a 'precautionary measures' suggestion). I'm still not 100% sure what the requirements are for this one... Anyone else?