what is the best way to travel from luoyang longmen to huangshan??

Hi, no direct transport can take you for this journey. I suggest you take a train to Nanjing first. Then you can catch a train to the mountain railway station. Upon your arrival, you can catch a bus nearby to the scenic area.

These days, it is cold there and the average temperature is around 0C. At the end of this month, the temperature will decline a lot. Meanwhile, it may snow then.

To be honest, it is tight to travel the mountain in one day. People usually get there and have an overview first. Then stay there for one night and travel next day.
Hope the information help!