Your guppy is neither (from what I can tell from the photo). Your guppy is just a bit chubby. You can tell if your guppy is pregnant as there will be a large black spot above their anal fin. The black spot are eggs which are waiting to hatch inside the female then be born live.
No, your tank is quite large and (apart from the Bristlenose) all those fish add a very small bio-load. Too many beginners spend too much time worrying about whether or not their tanks are over stocked instead of enjoying their tanks.