I was only in Spain for 3 months, but I lived in Barcelona and as a foreigner maybe I could give you some suggestions.
If those are your only 3 stipulations, you have a lot of options. I liked Barcelona, but I absolutely hated the amount of tourists (think Spring Break just nonstop in the summer months) and it is the most expensive city in Spain. I think I would have preferred to live in Sevilla or Madrid. Sevilla is so beautiful but extremely hot, affordable, and there are a lot of cool places to travel in Andalucia nearby (Cordoba, Malaga, Granada, etc.). Madrid was my absolute favorite city, it is gorgeous and there is just so much to do there, but it lacks a beach. Valencia would be another good choice, it just wasn't my favorite compared to those two, although it's very similar. The only other cities I visited were Granada and Zaragoza.
People are late in Spain too! The whole day starts pretty late - my work day was supposed to start at 10am but if I showed up at 10:20 I was still one of the very first people there. People are really laid back about that. The Siesta is also very real - the streets are quite dead in some places from about 4-6, but then everything will stay open quite late, with many restaurants open on weeknights until 1am. The kiss on the cheek when greeting is also a thing, and many European friends commented that they knew I was American because I didn't automatically do it when I was meeting people! You should also note that every part of Spain is very different from each other - Basque Country, Catalunya, Andalucia, etc. and each are pretty proud of their "province."
Spanish people aren't generally pretentious and don't care for foreigners that much. I think as long as you try to speak the language and take on the culture you'll be fine. I got called a "guiri" and "gringa" lovingly by my friends ;) "Guiri" just means tourist from what they've told me, I don't know anything about it having sleezy connotations. I found most people to be very warm though I was often mistaken of being Spanish, but when I would let them know they were speaking to fast for me, I always felt like they were still warm and then would ask me where I was from, etc. Spain is quite welcoming, and all kinds of travelers go there from Europe and both Americas.