What do I do after aluminum? It's overwhelming

So I recently unlocked aluminum and set up a small factory making the aluminum sheet and casings, but now I'm overwhelmed on what to do next. There's so many different factories that I could focus on but I'm not sure which would be the best. Should I focus on heavy modular frames? Computers? Set up a train system? Any advice from people who know this game better than me would be appreciated. Thanks