The book gives a few examples on which sort of Chaos Space Marines that can make up a given character and specifically mentions recently fallen loyalists and Storm Wardens (the "in-house" Space Marine chapter in Death Watch, p.50).

Now, I imagine playing one of these recently fallen Space Marines will precent a number of unique challenges and obstacles that a veteran Chaos Space Marine would not have to worry about.

Specifically I imagine that it would have to be one tough Space Marine to not end up as the plaything of a more "real" Chaos Space Marine. Skirmishes and out-right war between Space Marines is certainly nothing new in the Vortex but I still cannot shake the feeling that a previously loyal Space Marine that recently fell to chaos and made his way to the Vortex would be seen with very lustfilled/hatefilled eyes by a great many other Chaos Space Marines. Sort of like the new, young and fresh kid that ends up among the hardened criminals in an american jail (if I got my prejudice right).

How likely is he to survive the first few minutes in the Vortex?

How much more bad ass than the Chaos Marines does he have to become in order to stay alive?

Does it even make sense for him to make his way to the Vortex? And if not the Vortex, where would he likely escape the wrath of the Imperium (and his Chapter)?

You are correct in assuming in that Marines that have recently turned renegade have a harder time, especially those of a later founding (Marines of Second or later founding, whether loyalist or traitor, often have to deal with being called "Thin-Bloods" and "Mongrels" by Traitor Legionaires).

However, that does not mean that anyone would have the irrational urge to kill him at the first opportunity. Some Traitor Legionaires might demand some show or token of respect, but that is about it.

And even if he does get problems with "older Marines", he is still a Marine himself and being the protagonist of an RPG means he is "different from then" by default.

I think this is the first time I've heard of the concept that CSM will try to **** each other... but the prison analogy doesn't seem remotely accurate in any case since CSM are almost guaranteed to already have their every want provided by their employers.

Former loyalists will have fancier tech that may make them a target, whether for raiding, trading, or con jobs, though I imagine many legionnares take pride in using their HH era tech.

I'd expect a freshly traitorized marine to be a cut vastly above, though. Simply put, how else would a lone marine go anywhere between stars? Probably hijacked his own space ship to get there, and stole all the chapter goodies he could on the way out. Again, this could result in people wanting favors, or just trying to stage a raid.

"Turned" loyalists bring fresh gene-seed to the table- something desperately needed by the traitor legions, who don't have the endless resources of the Imperium to replenish their fallen numbers; so, I imagine a "new recruit" might be "courted" by existing CSMs to join their particular legion...

Well since the original chaos space marines have been existing for ten millenia in a state where linear time is a meaningless concept, and their entire reality has consisted of near constant fighting and general weirdness, I would imagine that reactions to more recent converts would vary dramatically depending on the individual and be generally quite unpredictable and ... well... chaotic.