Useful things to know:
Seasons: We’ve been there at the end of April - beginning of May and it was just perfect. The countryside was green and flowers were in bloom. It wasn’t too hot which was good for cycling though we have had some rain as well.
Roads: We tried to take smal roads as often as possible and they were mostly in a very good shape (thanks to EU structural funds :). They were also not very crowded. Most of the time we could cycle without being much disturbed. However as soon as we took a bigger road the traffic was much more dense with trucks passing by. If you have time you can nearly always find a secondary calm road that gets you to your destination. The Michelin indication of "sceneric roads" (green line on the map) was usually trustworthy.
Trains: There is no problem to take bikes on trains in Spain. It is a bit more tricky with tandems. If you ask those selling tickets they will be dubious. However we were always lucky and accepted by the controller.
Housing: We originally planned to camp. We were carrying all the necessary equipment with us for just one night in a camping. The problem is that there aren't many campings once you leave the coast. In addition you can find really cheap hotels (between 35 and 55€ per couple) so if you are not on a seriously low budget you can leave your tent at home.
Note that breakfast is usually not included.
Map: we were using the Michelin 1:200000 map of Andalousia. It was sufficient. We also bought the book "Cycle Touring in Spain: 8 Detailed Cycle Tours (Cicerone International Walking)" but honestly it was not very helpful. It only contains eight rather small tours.
People: They are nice and welcoming (specially to tandems :). However they do not speak much of anything else but Spanish (or Andalousian more percisely). But we always managed to get what we wanted with our five words of Spanish.