Travelling from Canada to Dabu, Meizhou, Meizhen, Haikou, Hainan, Guilin and Shenzhen only.

Travelling from Vancouver, Canada to these above destinations. If I want to visit Shenzhen last, can you please arrange them for me in order ? Is Hainan and Haikou in the same place? I like sea-shell. I heard that Hainan is a seashell paradise. Is there any beach in Hainan where I can find the treasure of sea shell on the shore? Will it be a good time to visit these places in April? What about February? Will it be cheaper to fly to Guangzhou first instead of HK?