AS level is intended so that you can have a wide range of subjects. Most students usually drop one of their AS levels at the end of the first year, but some do, of course, continue with all four of their subjects. Maths goes well with the two science courses. For the Language, I would advise choosing the one that you most enjoy. If you are finding it difficult to decide, it may be possible to switch the Spanish GCSE to Maths at AS level, as long as you are not intending to apply for a language at University level.