I'm not sure of your nationality, so I have no idea how you'd get a visa or if you'd need one. As a US passport holder, I was able to cross borders and enter both Croatia and Bosnia without a visa - just limit my stay to 90 days in Schengen countries.
In May 2015, I drove from Kotor to Mostar via the Bosnian town of Trebinje (it's in Hertezovina - so is Mostar). I spent a night in Trebinje - nice, untouristed town, with a beautiful old stone bridge - then on to Sarajevo through Mostar. I would say this drive between Kotor, Trebinje, and Mostar isn't incredibly scenic - not bad, but the scenery on the Bay of Kotor is amazing, and the drive from Mostar to Sarajevo along the Neretva River is also beautifully scenic, so the drive between Kotor-Trebinje-Mostar seems pretty ordinary, if pretty in parts.