Do I need primers if ordering from a DNA synthesis provider Do I need to design / synthesize primers for PCR if I am ordering from a DNA synthesis company and they are providing free cloning into my preferred vector backbone? Any good reason to order primers as well?

Only if you intend to subsequently amplify the DNA you've ordered. I tend to never fully trust anything I don't confirm myself so primers to sequence the insert in the construct they give you might not be a bad idea either.