NC LLC, DC registration and license question
Are we required to register and obtain a business license for this? What if this single transaction leads to a further contract?
A single transaction should not require you to register in DC, however if your relationship becomes more or less continuous, and it falls under DC definition of "doing business in the district" then you will need to register your NC LLC as a foreign entity in DC.
Since each jurisdiction has it's own rules and definitions of what constitutes "doing business in" it is hard to say at what point you will need to register, but such steps as renting an office or hiring a full time employee in DC would certainly mean your company is "doing business in DC".