Everything you could possibly want to know about Warhammer 40k: Eternal Crusade up to this point in time has been collected and published in a new FAQ on the official site. For instance, it is now official that Eternal Crusade will be "premium with a free to play option". There are also sections on units, lore, how to play with friends, release date and many others.
What classes are in the game?
Each faction features a unique selection of classes drawn from their lore, and each character in a faction has the opportunity to choose from a variety of classes when they deploy on the field.
For the Space Marine faction, a few of the classes you can choose from include Tactical Marines, Devastators, Assault Marines, or Apothecaries (Wolf Priests in the case of the Space Wolves).
Check out their codices if you want to speculate - more details soon!
Read the full FAQ on the Warhammer 40k: Eternal Crusade site.