Traveling in China over Easter

Hi there,
I'll be traveling to Xian - Beijing - Shanghai from late March to early April, should I be concerned about the weather? I've heard it's beautiful and the gardens blooming. we'll be pretty active, and I would guess that when we're in the city most restaurants etc will be heated. Also we're travelling from Beijing to Xian would you recommend the train? I've found the time table a bit confusing. it looks like it takes about 5-6 hours is that right? Any feedback or must see attractions would be appreciated cheers Kirstin