which i will then upload and release under a free license (which ones do you recommend in this case erik?)
Although I'm not Erik, I'd recommend you to use some of Creative Commons licenses (CC-BY or CC-BY-SA of any versions). GFDL is not very good for music. Also you can release it in public domain if you like to :)
*does it have to have a text, or can it also be just nice music? *in case of a text, which one is preferred?
This is purely my opinion that it doesn't. Wikimedia is an international organization, but text has to be on one language, so it possibly would be suitable in the first time, but then you will have to compose new songs for other languages.
— Kalan