Grammar check: “Welcome to A Firm, where great design converge w/ traditional craft.” Is it Design or Designs?

“Welcome to a firm where great design converges with traditional craft.” No comma after firm either. You could say designs, but to keep the sentence parallel you would have to say crafts as well. Converge needs to be converges. This is my way of answering. Hope it helps.

if there would have been `a` before great then design would come but as there is no letter ‘a ‘ before great so designs would come.