Iv'e pick dead space back up again to get through the achievements.  I've already beat the game on easy and only use the plasma cutter.  I see that my save slot of is title as "clear" meaning I've beat the game once but also saying "Round 2".  I do not remember what really this save file is.  Is Round 2 meaning I am playing the game through again on HARD or  impossible Mode?  Also I would like to say that did started playing the game on HARD mode today and dear god it is HARD!  
 
 Also I would to ask one more question.  I've downloaded some weapons for the game, will they show up when I buy new guns without having any credits or would I have to use credits to buy them?

The only thing I think i can answer you is for the DLC weapons. I downloaded the Elite suit and didn't have to pay any in game money to get it, so that leads me to believe the same is true for the rest of the DLC.