Public holidays are an absolute nightmare, RC, as you may have noticed! Aside from the national ones, there are regional (all of Galicia, for you), provincial (are you in A Coruña?), and your own municipality. But you also need to keep tabs on neighbouring municipalities. Let's say you live in a small village just outside Vigo . You might be on holiday for San Whatever, and go into Vigo, but it's not a holiday there, because they do San Something-Else instead. And vice versa. You will probably find that your local farmacia has free mini calendars marking who is 'de guardia' each day, which should also have the holidays for your municipality, including national, regional and provincial. That's your starting point. Online, search for 'calendario laboral' + whatever geographical designation you want, be it city, or province, and you should find something. But check the year - some of them can change from one year to the next depending on whether they fall at a weekend.

For cars, I would have to check. There is a big Stellantis (i.e Citroën, Peugeot, Fiat, Jeep, etc. conglomerate) plant in Vigo. But I don't know what models they manufacture/assemble there. That would probably be your most eco-friendly choice to buy local and support the local economy.