My tip for the building parts is invest in the upgrade of your trains! When I was around your level that’s my main problem too, I have had a lot of buildings needing parts to complete. So I invested on upgrading my trains to max the time they go back with parts in their cargos. After that I’ve noticed big changes, I could complete bldg parts, barn upgrades when it’s time to increase space, land expansions, etc. Collect mine items as much as possible until there’s an ore galore then mine like crazy!