Nope, no armor mods.
Speaking of REQ items, I'm SR16 and have only acquired 1 scorpion, 1 banshee, 1 wraith and 1 mantis in total to date (and maybe 1 rare variant of each), so I kind of grimace when I read other posts and advice on how to succeed in Firefight that basically come down to using power REQs every match that I just don't have to spend.
I really want to enjoy this mode, but the REQ system really doesn't help. Maybe something similar to it that relied upon cooldowns rather than pure RNG? I don't know, but I'm still into this mode for a while yet, but it'll be mostly loadout weapons and the occasional light vehicle or more plentiful heavy weapon for now. And because I can deplete my ammo quickly, even with high accuracy, I'll need to stick near REQ terminals to resupply.