I would have left the poly tunnel frame in place till you had more local experience to see if you would need it, there are some plants that need to be started growing in the colder months under cover then transplanted outdoors to finish fruiting and ripening.
It's funny I want to have a greenhouse like that one in the future so to see it cut into smaller pieces made me wish I could have taken it from you. Only problem is I am in Tasmania (Australia) so it would have been difficult. The garage looks very well built. You seem to have a very nicely sized house with useful spaces.
What part of Japan is this? We have been to Japan three times and visited many different areas because we have a Japanese daughter in law and two little granddaughters. Will you get some money for all the scrap metal?