Spain during Easter (March 20-29, 2016)

'Is there a city that would be an especially wonderful place to be during Easter (i.e. Granada or Seville)?' - Almost everyone could/would say Seville, but whether this - http://www.exploreseville.com/events/semana-santa.htm- is a wonder to you I would not know.

'Would 3-4 days there be enough or should I plan to stay for the whole week?' - Plenty to see and do for most, without Easter parades, for three or four days.

'Are there places to avoid because of crowds?' - As above. Obtain the itineraries for the parades and go elsewhere.

'Might there be service disruptions or limited services during the holiday?' - Almost certainly no, but what do you want to accomplish?

'Do hotel charges increase during this week?' - Certainly - and you possibly will not find, at this late stage, your 1st or 2nd choice accommodation, but I do not know what you budget for.

I'm going this year too! From my research (without personal experience . . . yet):

The celebrations are almost all in Andalusia and begin on Palm Sunday. The biggest are in Malaga and Sevilla. There are websites that list the celebrations - mostly processions - for each town. The last processions are on Friday night, with little or nothing happening on Saturday. There is a very special procession in Granada on Easter Sunday morning. Semana Santa ends with Easter Sunday on March 27. Easter Monday is not a holiday in Spain.

During festivals, it's hard to get rooms and prices are usually high season. There will be crowds (especially in Sevilla), but it's a special time to visit.

I will also be in Valencia from March 15-18 for Las Fallas. The festival ends on the 19th, but prices for 18th-19th were too high for me.

There is a lot more going on after Semana Santa. Another huge festival in Sevilla is Feria, about 3 weeks after Easter. There's a horse fair in Jerez (not anything like an American county fair), April 30-May 7; Cordoba Patios May 2-16. If I were going to be in Spain then, I'd try to see them all.

Thanks for your comments. That wiki page article was wonderful. I'll check out the fair in Jerez.