That is a good time to visit, late enough that the roads will be clear and not blocked by snow, early enough to be before rainy season. Based on an arrival in Kunming, I'd block this trip out as follows, focusing mostly on Yunnan/Sichuan.
5 days: Kunming arrival day and loop trip down to Jianshui and Yuanyang Rice Terraces and back to Kunming.
9 days: Dali, Shaxi, Lijiang, Tiger Leaping Gorge, Shangri-La.
8 days: Overland Shangri-La to Chengdu, via Daocheng/Yading Reserve, other Tibetan towns tbd, and Kangding.
2 days: Chengdu area
6 days: Xi'an and Beijing. Depart Beijing.
This is fast-paced and would improve by another 4-5 days to add a couple of things (Huashan, Pingyao) and give more breathing room with the transport. Or, omit Beijing and end things in Chengdu or Xi'an, saving Beijing for a future trip. It's unclear whether your month time frame is due to personal schedule, budget limitations, or visa limitations.