There aren't really any official rules to a monotype run, so I'll just try to answer some of your questions.
FIrst off, generally speaking most people consider trading pokemon in cheating, I personally prefer it this way because what fun is it if you get all the good Pokemon right off the bat?
Using other Pokemon? As long as you don't battle with them, i don't think there is any problem at all with this.
And lastly, this is all personal preference, i myself am doing a flying type run, and I've been used charmeleon the whole time up until he evolved. Other people i know don't really have a problem with this either, because otherwise how are you even going to get said Pangoro or Charizard?