Now I'm starting to think about the repairs & stuff. I think the very first choice I need to make is between copper & pex for re-plumbing (to be done while the crawl space is being cleaned out and floor reinsulated).
Does anyone here know of a forum or other source that focuses on and provides information for making green/sustainable choices for remodeling and repairing an existing house?
Pex. We've had it in our attic & walls for 23 years and it still looks as good as the original. You don't want to deal with pitting corrosion of copper piping, and pex is a lot easier to fix in a crawl space than solder or Sharkbite connectors. And as SamClem says, you'll be a lot happier with pex if it flexes or freezes.
The practice is to run pex through the walls/crawlspace/attic for most of the path, and then to change to copper for the last 6"-12" before the faucet connection.
I am only looking at plumbing because the existing pipe is 60-year-old galvanized iron and inspector says it is at the end of its useful lifespan. I might be able to live with it, but it seems like it would make sense to deal with it along with other crawlspace issues. If I run short of funds I will probably see if it (the water pressure etc) is tolerable and maybe have the re-plumbing done at same time as a future kitchen remodel, which will require crawlspace entry because it includes changes to the plumbing as well as extending the gas pipe to change the kitchen range from electric to gas.
Galvanized iron piping? Are you sure that's water supply, or is it a drain to the sewage system?
If it's a sewage drain then you could let it go for a long time because it doesn't see a lot of pressure. It's also easy to slice out large chunks of pipe (with a metal saw or a chain cutter) and replace them with rubber & hose clamps.
But if that's indeed pressurized water supply piping (bummer) then it's wise to do the work while you have the space open. Spending up front for that labor will save you lots of re-work over the coming years.
While you're replacing water supply piping, consider a water conditioner and a new water heater. You may not have hard water in your neighborhood, and your water heater may have some life left in it, but again the expense is in the labor and not the materials. It's a lot easier to spend the design time & effort up front (in conjunction with the work you have to do anyway) than to retrofit years later. Professional contractors refer to this foresight philosophy as "Might as well..." syndrome.
Since you've adopted an aging home, you may want to embark on the continuing education program of Family Handyman magazine. $10 at Amazon.com for a year's subscription.