Planning to stop in Mostar from Dubrovnik to Split drive - need suggestions/guidance

I'm headed to Croatia next week, starting in Dubrovnik for few days and then planning to drive to Split. I was thinking about getting a rental and stopping in Mostar on the way to Split. I've traveled a lot in Europe but this will be first time renting and driving solo in Europe. I've been researching online and here, and now confused if it makes sense to just take bus or ferry from Dub-->Split, and then rent a car in Split to do day trip to Mostar. Couple or questions:

1. I'm reading the border crossings can take few hours. Will it be this bad mid April, which is technically off peak time?
2. any other must see or doable stops on the drive from Dubrovnik ->Mostar->Split that I can fit in the day?

3. anything else to keep in mind about getting a rental or driving in general in Europe? I'm looking at using discovercars which seems to be highly reliable from

   what I've read so far.

Thank you.