Hello!
Right now it's not the best time to work in Rio (and Brazil). We're in the middle of a huge crisis, and a big part of the companies of the (before) emerging startup scene are in trouble. Of course there are still nice opportunities, but not as promising as it was from 2009 to 2013.
Most of the startups I know are in Botafogo or Barra.
Good luck,
Marcelo