Quick-connects for the 1/8" metal? Wow, that would probably be a lot of money for four of those. And I don't know how airtight they'd be. Or how sturdy. I wouldn't suggest that as an option.
As far as nipples ...trying to think of how to describe this is making my head hurt. I can't even tell if we agree or disagree on turn direction.
Best way to do this is go to Home Depot, buy a few 1/8" NPT pipe fittings from the plumbing department, and experiment.