13 Apr is viernes de Semana Santa a holiday for office workers and lots of stuff will be closed (Museums, etc.). Easter Monday is also a holiday. Good Friday Processions are all over Spain (including Madrid - near the Ayuntamiento (City Hall)). You can watch them on TVE or brave the crowds - it starts as a religious thing but ends with drinking, etc.
Most of the people who take Semana Santa off are back to work on Tuesday. School groups may still be crowding the Palacio Réal which you should visit in Madrid.
BTW
That's an ambitious itinerary for 8-days. Trying to fit in a visit to the Costa del Sol would be a bit much.
Sevila's Feria de abril is usually 2-weeks after Semana Santa - according to my calculations it begins 4/29, so that doesn't fit in your 8-days
[This message has been edited by Eddie (edited 03-14-2001).]