You need spanish lvl 4 because if you have to talk with other airport personal (fire brigade for example) they donīt have to sepak english.
Also, a private pilot (visual TFC) does not need to speak english to fly here. So lvl 4 is required.
The offer is to work on some towers, no idea about economic conditions but canīt be more than 50.000 eur per year, I think even less than that.