would like to asked you some info about the weather and some shopping places in shenzhen and shantou

1. The weather conditions will be similar of these two cities. The temperature may range from 60 F to 70 F during that period of time. It won't be too hot or too cold. The climate would be cool and comfortable. You don't need to bring thick winter clothes. Light jackets, long-sleeves, T-shirts and jeans are suitable.
2. In SZ: Many clothing wholesale markets are located in Luohu District, such as Dongmen Baima Clothing Market. You can go and see. It's located at North Renmin Road.
In Shantou: The Square Clothes Market is a nice one. The location is No.4, Li'an Road, Jinping District.

Can i ask you some info about any nice food at SZ?

Yes! The delicious local food includes seafood, sausage, roast goose, roast pigeon, etc. Have a try! :)

i wanna ask bout the train seats from shenzhen north to chaoshan...actually the train is how many seats in 1 row ? is it 3 seats in 1 row or 4 seats on 1 row? i was a bit curious coz i bought the train tickets is row 17D,17C and 17F..

Oh, you have bought second class seats, right? In second-class carriage, there are five seats in one row: A, B, C, D, F.
A, B, C are in one side of the aisle with C next to the aisle, and D, F in the other side with D next to the aisle and F to the window. FYI: https://www.travelchinaguide.com/china-trains/types.htm