They might have been sergeants, and then there should have been roughly 1/10 (if they want to be consistent with how it works in tabletop, though some regiments have more, and some have far less, there is no real standardization in IG, not even in regards to what weapons they use), but yes I agree, it felt like there were too many of them. I'm not defending the game itself though, there is no real reason to play it.
No, the commissar cadet/training squads were sadly removed from the game with the release of 3rd edition, and have never been re-introduced (as far as I know). You could probably represent them by using veterans or even penal legions though. I've not played 40k in about a year though, I switched over to battletech, as I was more than a tad bit annoyed by how GW treated their games (the current armies are rather bloated. While I do welcome the fact that they are trying to give people more options, it feels like they are not even trying to balance things, so at times it feels like playing 5th edition fantasy all over again. And they also made transports a no-brainer, which means that all you face at the moment is transport based armies), so they might have re-introduced them since, though I doubt it. GW dislikes introducing new units outside of new codexes these days (so there is even less of a reason to buy WD).
That is an alright model. It would probably have looked better with a helmet on though. Its choice of weapon makes it unsuitable for actual use (pulse carbines are utter junk)