A little surprised you are taking the train from Barc to Seville as this is a distance and time consumption to which we typically fly.
Pick up the car when you are prepared to depart Seville. Pick up your IDP at AAA, $20, before you arrive in Spain as it is legally required to drive in Spain.
We base out of Malaga and have a car so here are some travel thoughts.
From Seville drive to Ronda. BTW: bring a black single sheet to use to cover your luggage. We use a hatchback which has a cover to reduce opportunity for thieves to view what is in the car. Be sure and obtain a GPS. Spain, and most of Europe, heavily relies upon cameras to catch traffic offenders. Be very wise about obeying all traffic laws. We strive to park outside of tourist zones to avoid driving in the narrow clogged streets of an old town setting.
Use the internet to pull up Michelin map web site and strive to get familiar with potential routes.
http://www.viamichelin.com/web/Maps/Map-Spain
In early March sundown comes early so DO NOT take hwy A-397 down to Marbella, from Ronda, (less then two hour drive) as this is a narrow two lane highway. If you were to be in daylight then this route offers terrific views, especially of Gibraltar. Take A-366 and it is an easy drive in Malaga (less than two hour drive).
From Malaga to Granada is a two hour drive an you have several route choices. To Granada I recommend the coastal route, returning the inland route. In Granada you will want to use the public parking lot at the top of the hill and at the back of the Alhambra area. Do your homework using google earth aerial to understand the route. It is VITAL you immediately invest in reading on how to tour, navigate and obtain tickets using a variety of web resources. REPEAT, VITAL!!!! We encourage staying to watch the sunset across from Alhambra.
We love Malaga and greatly enjoyed walking through the old town, the fort, marina, market and often get away from worn tourists paths to explore restaurants occupied by locales. A great town.
Check the fubol schedule for a chance to attend a game in Malaga or Granada.
March will still be a little cool in Granada (Spain is experiencing a very cold winter this year with a lot of cold snaps). The Sierra Nevada mountains will likely still be covered in snow.
Be very aware of pick pocket protection during your entire journey in Spain.