Hey!
I'm currently studying four A2 levels, and am considering not taking up my university offers for Literature, taking a gap year, and applying to Medicine. In that respect, taking enough A Levels to allow for a change of heart has been brilliant. I also do a language, German, and it's brilliant because it provides a contrast to my other studies without being useless, and so if you will find Spanish easy, I'd really recommend you go for it! Doing four hasn't really been too difficult, and I've managed to do an EPQ and various other things, despite not being superbly intelligent, so as long as you don't let it affect your mental health too much, I've found it almost encouraging, as I have the option of screwing up on a paper and still managing to get into uni based on my other grades (though hopefully I won't!).
One of my friends took up one of the linear A-Levels to fill a space on her timetable after having completed maths A-Level in one year last year, and because she will be going to university instead of continuing the subject to A2, she will get an AS in that subject - apparently the only way the AS won't count for anything is if you continue to A2. It's a strange system, but that's how it's working for Business and I think for the rest of the curriculum too, so I think while you would be encouraged by teachers to continue with a subject for two years, you by no means have to!
Hope this helps!