What do you have in mind? Are you planning a long scarf with the ends joined? The Kitchener stitch is used to join live stitches seamlessly. It would provide the least noticeable joining of the ends. If you cast on normally and then bind off at the end and seam the ends together, it would be more noticeable. I think your plan for the provisional cast on is a good one and it's a good skill to have. It comes in handy lots of times. And yes, I think Kitchener would be better than 3 needle bind off here.
I should never overestimate my basic arithmetic skills.