May I know why you play exclusively NU? Some love for the forgotten?
I was watching a Pokémon Showdown recorded battle on YouTube and the guy was boasting about winning with his Sandslash in OU. Thing is, the rest of his team was top-notch OU (stuff like Tyranitar, Ferrothorn, Heatran, etc.) and half the other guy's team was the same! It gets really tiresome. My only contact with simulators was back in GSC when everyone used Snorlax, which was the undisputed best Pokémon that wasn't uber, and God I hated it so much.
So I perfectly understand why you only play NU, although I can't help but feel it's a little depressing to see some of my favorites like Braviary and Charizard in the "worst tier" of sorts.
About the infraction, I'm behaving here far more than in other places, because I've been to all kinds of forums and there's some stuff you can say in some that you can't say in others. Here the moderation does a great job of keeping the threads where they should be, but it can get confusing for a newbie since the forum is HUGE!
Anyway, yeah you can use any of them except for the one White Kyurem one, although I'm not sure it'll display in your avatar, given that there's size limits, and such.
For two, it was just a warning so it was just an advisor to not do something along those lines in the future (it won't disappear as it's there for reference but ya). Just be a good member and you have nothing to worry about :3
Uhh higher staff did although I technically complained about B/W's activity the day before being told about it so that might've helped lool. But yeah, adventures in unova is going to be an awesome forum imo.