There's factories with infinite supply simply because no one knows where they're getting it from, it's old world tech (not to mention it's too dangerous for anyone to actually discover and take over those factories, much less figure out where they're getting their resources from). And it's also not important from the PoV of the new world hunters that are just out there to make a quick buck.
And questioning about why its mostly guns and not melee? Well it's sci-fi, and just look at the world today, where are all the close-ranged weapons? Instead, you should be asking why for such an advanced civilization they're still using projectile weapons.
As for the stress on his body, that's what the meds are for. The nanobots are supposedly fixing him up as fast as the stress he's being put under. If none of this makes sense, just read the novel.