My main question is: why English? For a better chance at publishing? I'm not suggesting it should or shouldn't be in one language or another - your English is phenomenal, but I think it merits an explanation (at least for yourself). I think it makes MORE sense to write it in Portuguese and then translate it, because it will likely match your intentions more closely if you do it that way, and tiny mistakes will be much easier to correct, because you will have the original Portuguese to compare it to when editing.

I know that is what Ken Liu does - he writes in English (his native language) and then translates it (himself) into Chinese. I'm sure there are plenty of other bilingual writers, but his is the only process I can speak to re:translating during the writing process.