I'd suggest you don't try to do everything; having a small set of languages but being able to use them for their full potential would be better IMHO.
With that in mind, >>892 has some sound advice on which languages. Also, Portuguese would be a really easy option for you (+1 language for the price of 1/4!).
(Por exemplo: aposto que consegues entender esta frase sem saber português, apenas pelos teus conhecimentos de espanhol/castelhano e francês.)