It's Bach, so the choice of a tempo is really up to you. I think Gould played it at about mm=66, but I've heard it played much faster. Bach didn't assign any tempi to his music. My suggestion is to play it no faster than you can produce beautiful tone. One of Bach's avowed purposes for writing the inventions was to teach the production of beautiful tone. Of course that was on the clavicord, but still I think it carries over to the piano. Bach is uniquely useful in learning to produce beautiful, bel canto tone and learning to play legato.