Some thoughts.....
In Spain we often rented cars and enjoyed success with internal and external gps systems. Over the years the systems technology has become more intuitive = easier and more accurate to utilize.
That said, no matter how good the system attempting to use gps in an old town district (like Seville) is quite disfunctional as you are driving in tight quarters with a lot of distractions and often small unfamiliar signs to follow.
We recommend going to the web site Via Michelin to plan your trip
https://www.viamichelin.com/
And most important we recommend using the Google Earth Street View to follow the path of the journey you mapped using via michelin. By doing so you can become familiar with "markers" defining key intersections/turns to have an idea of where you are heading. For example if you need to exit a highway you can view what the buildings look like at the departure point so you have a visual aide to recognize you are in the right place. Time spent doing this exercise enhances your driving confidence and reduces the time staring at the gps trying to confirm you are at the right place. Yep, the gps voice will be talking to you about where you should turn, but I like the affirmation of seeing a recognizable landmark.
We preferre renting a hatchback so the lid could hide the view to what is in the rear of the hatchback. We also carried a single black bed sheet to cover items placed in the second row passenger seat.
Depending upon the time of year items kept in a car can quickly melt (angry wife = expensive melted cosmetics). We rented cars to take the time to explore getting off the beaten path, but if your intent is to go from point A to B the bus and train service provides a less stressful experience.
BTW..... please comply with Spanish law and obtain an International Drivers Permit which you can get for $20 and a passport type photo from AAA. Essentially this is a rehash of your drivers license blended with your passport info, but it is legally required by Spanish law. Most important be aware many traffic fines are due in cash and on the spot of where the infraction occurs.