There isn't even Dominator in this first patch. I think 3rd class is only added later. Either way, you probably won't get there that fast. They will probably launch 2 or 3 patches until you reach 76, and that is being optimistic.
And Overlord is not really good until it becomes a Dominator, so I would suggest you concentrate your strenght in lvling a spoiler/crafter/buffer first, and then power level an Overlord into a Dominator as suggested by @FatHips.
But hey, the main goal is to have fun, so if you like to play with OL, forget what we said and go for it. Every class is needed, useful and important at some point in the game.
