It's a beautiful historic city accessible by fast train.
Dress code for churches: Shorts or bare shoulders are not allowed for either women or men.
Must see places are the Royal Palace, Museum, Thyssen Museum, Reina Sofia Museum, National Archaeological Museum, Sorolla Museum, Cerralbo Museum, , El Retiro Park, Basilica of San Francisco El Grande.
My personal preference would be to allow time in Seville by reducing time in.
The north will be a trip for a later date.
A taxi to the Mezquita will cost only about 6 euros because the distance from the train station is only 1.