Era 5 Preparation

Level up your Laboratory. Level 25 is needed to get Era 5 Coupling by the end of Era 5 without a plus account. Level 22 is needed with a plus account.
Be sure to save enough money (7,500,000) to upgrade your Engine shed right after we hit Era 5.
Get Coupling. If you won't have Coupling by Era 5 but you can get it less than a day into Era 5, you should finish the research for it. 1 to 2 days is more questionable but I wouldn't blame you for getting Coupling. More than 2 days, IMO forget about Coupling and save your research points for Era 5.
Have at least 5-6 free tracks to begin Era 5. Or connect to all Era 5 RGs by using a Map Of Goods.