Trade only: Yes, you go first.
In my opinion disenchanting other classes cards is always a bad idea. Try to start with F2P decks you can find here, grind in Arena and gradually you will be able to play multiple decks ;)
Another disadvantage of playing a single class is that is hard to you to understand the strongs and weekness of all the other classes.
Good luck with the first steps
I love all the classes.
Each one as it pros/cons and different playstyle but i guess every mom as his favorite son.
Mine is Paladin(2000 Wins). My less played class and the only one I don't have in gold is Shaman (400wins). I don't have all the cards from last expansions and I really don't like the new archetypes.