I myself used the +3 Rate of fire +2 Damage circuits on my gun's top board and it was essentially a hand cannon that shoots at a ridiculous rate. it is possible to collect a full set of a type of artifact which unlocks certain circuits that you can craft and then use for the rest of the campaign. With still a fairly sizable chunk of the campaign remaining. eventually you should aim to have damage full and pile everything else that you can (on the top circuit board) to rate of fire. The bottom circuit board on the plasma cutter seems to be only effected by reload circuits, so putting anything else there is just a waste. The first chance you get you should upgrade the plasma cutter with 4 +1 Damage +1 Rate of Fire circuits on the top circuit board and 4 +1 Reload circuits on the bottom. The difficulty is automatically set for hard (which when you beat the game on impossible and go to hard afterwards, doesn't seem all that terribly hard) In this game mode, the difference from the standard campaign is that only classic weapons are available for crafting (i.e no acid attachments, or anything that was introduced in Deadspace 3 to the player) You begin with a plasma cutter which i suggest using throughout the campaign as your main (and if you so chose) only weapon. You start completely anew with no items from your previous save. This is under New Game+ once you beat the campaign for the first time. This achievement is for beating the game on Classic Mode.

Dead space 3 plasma cutter model