A business plan is the best place to start. I started out and continue to use Overdrive's "Partners in Business" manual for owner operators and small fleet owners. It does require some modification for expediting, as it was written mainly for the tractor-trailer crowd. I definitely plug figures into my plan as I go along, to get better ideas of what makes good financial sense. Working on the road, it's hard to keep much in your head. If you keep accurate records (receipts, etc) you can do most of it yourself when you have time at home.
Find a good accountant who lives nearby you who has some knowledge of the trucking field. It's best to meet face to face on the tax subject, not merely send your records to someone you don't know.
It takes too much time to clarify cloudy things.
You won't need an attorney, most likely, to start out.
-Weave-