Depending on how easy it is to take it all down. You can take it into a Ace Hardware with the measurements for any piping, and they can cut & thread for you. If you cut it, use a motorized handheld band saw with a Metal/Steel blade. You can also rent the motorized threader/cutter, so you can do them on the fly downstairs.
Any leftover piping, just do like I do. I toss all of my extra stuff that is long enough, up on top of the trusses in my garage. I actually bartered with my plumber, when I had my water heater put in. Because we found some Black Iron & Copper pipe that the original owners had tossed up on top of the trusses.
For some reason with my setup, they got lazy with one section and just used a Black Iron Pressure fitting clamp to join the two sections, instead of threading them, to use a threaded coupling.