I´m from Barcelona.I bought my flat a long time ago, from what I remember it goes region by region the amount of tax you pay to regional government, council tax to the village/city etc . You need to add service charge for the flat if it´s in a block of flats, service charge for a garage if the flat has a parking space, etc etc
Barcelona and Sitges attract lots of tourists and city workers internationally, Valencia also attracts national tourism. Prices change depending on the neighbourhood and square metres you buy and if it´s a very touristic area or for local people.
Airbnb is regulated and in some buildings the community of people living there agree against it and you may not be able to rent your flat to tourists as it will go against the community.
The contract agreement works different to UK, when you make a deal and place a deposit in advance they must sell the property to you,if they dont then they must return x 2 the deposit. It´s called "contrato de arras".
Get the advice of property managers services or lawyers , quantity surveyors etc
They aren´t as expensive as in UK.
Good luck, send me a message if you want to know more or need help to find info about neighbourhoods etc.