Honestly for the dollar investment involved you might recommend that he pick up the Dark Angels half of the Dark Vengeance Box set from ebay.
For about $50 you can get x10 tactical marines, x5 Deathwing Terminators, x3 Ravenwing Bikers & the Librarian.
That will provide a solid base from which to experiment and more importantly help your friend identify which units he favors before dumping a ton of money on anything.
No sense buying in a Deathwing or Ravenwing direction only to find out later the grass is greener on the other side
Hope that helps.