Tiers and leveling in Warhammer Online

I am interested in tiers and leveling in Warhammer Online. I would like to start playing this game, but I dont know where to begin. My initial idea was to look at the release dates and figure out what is the first tier of Warhammer Online, but then again it would be smarter to simply ask people who already play. So, where should I start?

Before I answer I think that is not necessary to start with first edition, which is by the way Warhammer: Shadow of the Horned Rat dating back to 1995. It is much more interested to begin with the last edition, being Warhammer: Mark of Chaos. It is more fun then the first one, but it is also more difficult then starting from the beginning. Dont think that this way you are going to be far behind people that started from 1995 edition. But this way you will have fresh look at things and that is your advantage. Trust me, and you will do just fine.