You can find direct bus from Yiwu Binwang Long-distance bus station to Tunxi, Huangshan. Or you can take train from Yiwu to Huangshan via Xuancheng.
The weather in Huangshan in early April is generally rainy, misty and cloudy. The average temperature is about 10C. It is cool and warm clothes are needed.

Thanks Sara, How long does it take by bus/train from Yiwu to Huangshan? When is the best time to visit Huangshan?

The bus journey from Yiwu to Mt. Huangshan will take you about 5 hours. In fact, this mountains could be visit through a year since it has unique scenery in different time. Considerating security, summer of May to early Sep will be recommended.