1) No idea. I think it must, because I get the same number of criticals when doing 5, separating out 1 at a time as I do a stack of 5. I have tested this 42 times so far, so by no means definitive yet, as crits vary in frequency. However, it's looking to me as each item in the stack is getting a crit check. 2) and 3). The long answer is in the sticky- choosing your professions. Money makers and what goes with what, and what they mean. Short answer- take 2 mission running skills with your slicing. That said, on my slicer I also took bioanalysis and scavenging, since many mobs can be harvested as one or the other. Also, those gathering items sell, and missions can be run in both.