Just now moving to Valencia is not a great idea, they haver the worst record in the whole of Spain for lands grabs/corruption/ etc., ist one o fthe most expensive places also, may look very glam, but that doesn't pay bills!
1. Renting out is a very good idea. Use a reputable agent or go see a lawyer. Making a will is a good idea too.
2. Wages. They take about one fifth off you. 20K is a bit basic. BUT in Spain wages are often quoted net, not gross. Check this. Do you get the 'plus' for Christmas and August? Some places pay 14 times a year. Double at Christmas and August. Average Spanish wages are around