I don't really think the advances need to be bought in any particular order.  The unnatural strength and toughness are the most powerful marine advances, so it makes sense that they take the longest to really activate at full power.  Taking bulging biceps will lead to an increase in muscle mass, but not enough to be unnatural strength.  (yet)<br/><br/>I should also note that the black carapace has been intentionally not placed in the Rogue Marine advance table, because it's the last implant installed and can only possibly be purchased as an elite advance.  (usually with the help of chaos space marines, if the majority of the character's space marine implants are active)<br/><br/>As another note, the corruption rules assume your character is holding to the Imperial faith and consciously resisting corruption.  If your character chooses to accept the possibility of damnation, you'll become a lot more resistant to mutation, because the dark powers don't want to destroy you (quickly) but much more susceptible to demonic possession and insanity.  In game terms, if you accept damnation, you use the corruption track from the Radical's handbook instead of the one from Rogue Trader.  A character who accepts damnation can never possess the true faith talent or any talents that use it as prerequisites, and loses any talents of that type after choosing damnation.  Choosing damnation can be reversed by a particularly strong act of faith and burning a fate point, which grants the character doing so the True Faith talent.<br/><br/>As a side note, after a sufficiently miraculous event, a character may purchase the true faith talent for 1,000xp as an elite advance.  Talents which require true faith as a prerequisite may then be purchased at 750xp each, as the character grows in faith.  This cost may be discounted for characters who experience particularly impressive miracles or burn fate points to get new faith talents.