So... what exactly are the attack ranges and such we should keep in mind? And move speeds, for that matter.
Eh, there's no hard ranges. It's a subjective thing because it's not like I can say "at 150 feet your difficulty roll is 145" or something. Varies by weapon type and stuff.
Assume you can run about as fast as a human, that melee range is about 10 feet or so (because we assume you can cross 10 feet basically instantly) and that ranges...are quite vague but shooting things far away is harder.
Here's out arena
Red team, who is all standing around in a clump, you find yourselves in an almost pitch black room, the only light- a smoldering red glow- coming from a square doorway straight ahead. In this dull sanguine light you can make out heaping piles of rusty scrap metal all around you. Some of it is structural- I-beams, square plates, rebar in random lengths- but the vast majority of it is just horribly shredded, rusty metal shrapnel. The kind of stuff that could split your flesh to the bone and give you tetanus from a distance. The metal is moving as well, clumping up into rust-bunny piles and rolling across the ground with an unpleasant clink-clank-screech. It's piling itself onto a conveyor belt that leads on into the room straight ahead.
Blue team, who is all in a clump as well, you are standing on the outskirts of an assembly line. The room is a long one lit by scattered and irregularly spaced halogen bulbs. A conveyor belt runs down the center of it, flanked on either side by robotic limbs. These limbs are all moving at once in a dizzying display of coordinated action, building and attaching, manipulating the things on the belt. These things, whatever they are, are all different from one another. They look like mechanical things, like cars maybe, but deformed, the mechanisms crushed into strange shapes. Looking at them, they don't look like they'd actually do anything if turned on, but something about their shape is unsettlingly organic, despite the mechanical construction. Parts and pieces for the robotic arms are being shoved out of slots high on the walls, near the ceiling, and collecting in chaotic piles near the base of the limbs. The only visible way in and out of this room is the conveyor belt itself, there don't seem to be any other doors.