I own a lot of tools too (I do pretty much all of my own car maintenance - including replacing the head gaskets (a 2 month project I wouldn't do again)), but I doubt that is more environmentally sustainable than hiring experts (with their own tools), and I'm not saving any money unless I count my own labor as "free".
If you working on that car meant that it wasn't scrapped, if the job you did for free was a job that a pro would charge more for than the car's value, then owning the tools to replace head gaskets is the more environmental approach. The energy needed to generate a new car from base metals is immense.
I guess we have to draw a line between those minimalists who want to just own fewer things for the zen of reduced clutter, and those who equate minimalism with efficiency or anti-consumerism. That's why the Amish still own and use modern tools. Their minimalism is more practical than ideological.
I own a lot of tools too (I do pretty much all of my own car maintenance - including replacing the head gaskets (a 2 month project I wouldn't do again)), but I doubt that is more environmentally sustainable than hiring experts (with their own tools), and I'm not saving any money unless I count my own labor as "free".