It's not viewed as unprofessional in Brazil. It just has to be the right color for you. There's nothing more horrendously unstylish. They're discreet, chic and virtually indestructible. Don't carry a backpack, unless it sports a famous European label.
Evening bags are only for very formal affairs.
Leave your real stuff at home. But Brazilians have a flair for colors that Americans cannot match. So, stick to neutrals and black and white. You can't go wrong there, and, in any case, they travel well and mix and match easily. If you're going to be in Brazil for a while, I'm sure you'll see something you can't live without.