There's a difference between Chaos Marines and Renegade Marines. Chaos marines (like the World Eaters and Iron Warriors) and have been corrupted by the Warp powers, and all of thier chapters were a part of the Horus Heresy. Renegade Marines (like the Lost and Damned, and the early Lamenters), are not necessarily corrupted, but are, well, controversial.
My marine is from the Ultramarines, attached to the Deathwatch (a part of the Ordo Xenos of the Inquisition, elite alien hunters).
The Emperor eating souls is correct, it's called soul binding, and it is a part of the Astronomican, the psykic navigational beacon used for space travel.
The Adeptus Astartes (Space Marines), have no historical equivalent. The equivalent of the US Army Rangers would be the Cadian IG, the Red Army=Valhallens, Nazi SS=Mordian Iron Guard, SAS, Seals=Stormtroopers, etc...
The Marines are genetically engineered, 7 foot tall, CONSTANTLY trained, super soldiers. They never rest, never stop fighting. Heck, they don't even really need to sleep. WH40K is an incredibly rich universe, some of it is disturbing, most of it is REALLY cool.