You only need certificates on certain weight classes of vehicles. Unless you have a BIG Dump truck, you will most likely not fall into this class. Its mainly trucks over 2 or 2 1/2 tons or something.
As far as commercial work, most companies I have and deal with require ATLEAST Your EIN/Tax ID number for the company, www.irs.gov
to apply for it, then you can get your business license.... Insurance companies are also going to require your EIN/Tax ID number.
I have had some companies require me to provide proof of workers comp insurance.
As stated, make sure what ever vehicle you are Working with, is on your business policy!!!