For Spanish, I believe that you can start anytime (if you have a little Spanish). Go along and ask, whist there perhaps you could offer exchange classes with the students learning english. You have to ask the secretaria permission to stick a notice up but generally is’t not a problem.
I don’t know personally any of the language schools in Vigo. Here in A Coruña lots of the private language academies offer spanish for foreigners aswell as english for Spaniards. Don’t be put off by the fact that nothing will be in English in class - it works well just in Spanish.
Get youself a good spanish-english dictionary and I’d suggest a Spanish secondary school dictionary aswell. In the spanish part of the spanish-english, study the part on pronunciation, spanish is phonetic, so once you learn the basic sounds you speak as you read (unlike english). Practice reading, pronunciation and comprehension by buying a newspaper every day - El Faro de Vigo or La Voz de Galicia would be my recommendations.
When I arrived in Spain for the first time I arrived in March, without knowing anything in Spanish. I signed up in the EOI in April at the basic level - the course finished in June, but it was a start. I signed up for the same entry level course in September aswell, because I had missed the first 7 months of the course. In September, before the start of the EOI course, I signed myself up for a one week intensive total immersion course in Santander. This included four hours in the morning, four in the afternoon, lunch with the teacher in a restaurant in town and lodgings with a Spanish family. It was 10 years ago now, and wasn’t very cheap. I didn’t come away from that being able to speak Spanish, but my understanding was much much better: once I came back to A Coruña I found that I could follow my Spanish friends’ conversations much more easily. I´m sure that this one week intensive course was worth doing, when I did it; I had studied somthing of the basics: SER & ESTAR, regular verb construction in present, perfect and future tense. Probably taking the intensive course before having these basics would have been a waste of money.
Good luck with it.