What would you recommend to visit in Spain first of all?

Barcelona for sure! And also beautiful cities in the south like Sevilla, Granada and Cordoba! I was also really impressed by Toledo and Segovia❤️ Really wish to visit the northern parts of the country — sure they have their amazing pearls as well!!!

Barcelona and all the cities of El Andalus — Sevilha, Cordova and Granada for the history and atmosphere

I would recommend Mallorca.
I like to come there in Winter. The weather is still nice. Lots of places are shut. If you like hiking and cycling this is the best place and time. Bike rentals are cheap.