Rank is based solely on turns taken, you can kill one enemy and still get an A.
Status effects dissapear at the end of your turn, I don't remember there being a way to remove them manually, though some characters have traits that make them immune to status effects.
Shamrock weapon is just preference and what you'll be using it for. I had it set to flamethrower ever since I got to take out groups of units, but on some missions I swapped out to anti-tank stuff.
Some of the reporter stories have battles in them, but other then that it's just more story to enjoy. You have shedloads of money even buying every weapon each chapter anyway, so there's no reason not to buy them.
Interception fire is dependant on what class your unit is, Shocktroopers have abyssmal range, Scouts and Engineers should intercept at a decent range but they just have to be facing the right way. Snipers and Lancers don't ever fire on moving enemies.
Destroying tank treads severely lowers its AP, making them barely able to move far (although most of the time they barely move anyway, so I find it useless).
When a character loses it's HP, it'll be KO'd for 3 turns, if you don't call a Medic by then they die permanently. If an enemy steps on the body before 3 turns are up they die permanently. You'll know they're dead because you get a little mini cutscene with them saying some depressing shit, then it'll tell you they've died as opposed to the usual "Name has retreated." Story characters can't die, but I think once they're retreated from a "death" you can't call them back from a base that battle, but I could be wrong there. If the Shamrock blows up it can't be used for the rest of the mission, but it'll be back on the next one.
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