can I get to bedaling section by public transport?

Yes, of course. You can choose to take bus or train. By bus, you need to go to Deshengmeng. There you can take no. 877 or 919 bus to Badaling directly. It takes around 1.5 hours. If you plan to take train, you need to reach Beijing North Railway Station. There you can take S2 train. It takes around 1 to 1.5 hours.

The average temperature is fom 0 to 12 Celsius degrees. But the temperature on the wall might be lower because it's a bit far from the city. I think you'd better wear sweater, thick jacket, wind coat and other warm clothes. By the way, don't forget to wear a pair of comfortable sports shoes. It's convenient for you to climb the wall.