Not sure what season it is in Portugal, way up here it's not the best time of year to cut. I don't make many stave bows, but the best time to cut is spring and early summer, when the sap is running. I usually split, peel the bark, then seal the ends.
I think oak is okay to use sap wood just under bark, but I'm not positive. Somebody with more stave experience will chime in, i hope.
And Welcome to PA, if nobody has said that yet. This is a great place!
Tattoo Dave