I think I may have stayed in one 4-star hotel in Europe, but only because there weren't last-minute rooms available in cheaper places that had air conditioning (would not typically be an issue in Spain, where a/c is needed for multiple months each year). In Spain I stayed in a lot of 2-star places which tended to be small (sometimes extremely so) but were similar to some Italian 3-star places. At the 2-star level you often get decor that I describe as "recently redecorated dorm room." I never ran into that at the 3-star level, but the rating criteria vary from country to country, and many of the rating factors are simple yes/no or numbers-driven issues rather than evaluations based on things like charm and style. Is there a restaurant? Is there room service? How many square feet is the room? Do the toiletries come in individual bottles, or is there a dispenser mounted on the wall?
The 3-star places I stayed at in Spain would not have upset anyone, but some were more charming than others, and none had room service. What you can do is go to one of the hotel websites (I use booking.com), select a variety of hotels including the ones listed in your previous post, look at a bunch of the pictures and read a lot of the reviews. You may find places that you think would fully meet your needs down at the 3-star level. Or not, if you are the sort of traveler who regularly stays at Marriotts and places in that (or higher) price categories.
Train service from Madrid to Cordoba to Seville is very fast. I wouldn't even think of driving that route. You might like to have a car for your time between Seville and Granada, for visiting Ronda and some of the white villages like Arcos de la Frontera. I suspect, but do not know for sure, that you would not be allowed to take a rental car on the ferry to Tangiers (not that you'd want to drive in that city, anyway), but it could save time in getting to a parking lot near the ferry embarkation point (check on parking ahead of time).
If you are not time-limited, I urge you to extend your trip. Spain has many wonderful sights, and you will be very glad to have the extra time once you get there. Toledo, Segovia and Cuenca are three fabulous cities that are worth overnights but can be visited on day trips from Madrid. I spent two months in Spain this summer and did not even get to Andalucía, just to give you an idea.
A good current guidebook will generally tell you at which sights you'll need tickets purchased in advance (definitely the Alhambra and I assume the horse show) and at which you'll be able to bypass a long line by having pre-purchased tickets. Folks who've been to Andalucía recently can also provide guidance if you list the places you want to go. Like you, I prefer to wait till I'm on the scene to buy most of my tickets. But you'll probably miss out on a few high-demand sights if you do nothing in advance.