Adverb placement is not set in stone I suppose, but "He works slowly" really is the best way to say this. Here's some general advice: http://grammarist.com/grammar/adverbs/ (the relevant rule here is: "An adverb modifying an intransitive verb should immediately follow its verb").
Your guess is as good as mine. It might be a thing depending on which region (or state) of Brazil the speakers are from. I've heard some visitors say "sete" without emphasizing the "t" while others emphasize the letter "s" as an "shh" sound.