Is it better to visit Songshan+Shaolin temple from Zhengzhou or Luoyang as I'm going to both?

You can go to Songshan and the Temple from Luoyang. There are several direct tourist buses at the opposite of Luoyang Railway Station that can take you to the scenic area. The trip takes around 1.5 hours. And the ticket fare is around CNY 20 per person. Have a nice trip!