Challenge insights?

I have looked over and it is tedious to keep looking, but what exactly is needed to get the first aid medals? Is that the 5/10/15 revives medals in a game or what is it exactly? And also it seems for some reason, that no matter what I do I keep getting getting 0% towards cerberus troopers, when its rather obvious in a game troopers are going to be there getting killed especially when I solo. Also lastly is there different banners for completing the same set of challenges twice, I got biotic mastery already, and and over 70% of completing it again. I do not wish to grind on something especially when I am more of a tech player.