By power playing you mean overpowering the character to the point of total dominance, or atleast displaying the characters power all the time and therefor making no fun of the character and most likely making others dislike the character and loose interest? 

Don't worry, I will not. I, personally will man a veteran of battle, however we all know that all fall flat on their faces in certain times. Plus, not even Veteran Space Marines can survive truly overwhelming odds, unless you're Dante, who has plot armour. THANKS FLUFF.

Also, in this scenario, Are we roleplaying a squad? Since the Black Templars use their unique squad system with one veteran acting as the leading figure surrounded by novices, will I be roleplaying all these figures (5, I believe.) if the squad thing is ago?