When to destroy old factorys or use them for new parts?

Im late phase 4 now and ive completed every milestone till tier 8 and till now ive basically built a new factory for every new part and used new resource nodes but slowly im running out of nodes and I have to collect them from kilometers away so I wondered when I have to start using old factorys to craft project parts for example. ( I automated every item except the project parts in phase 4). Do you have any tips or ideas?