It's gonna be hot and humid in the south! Dress accordingly and bring ways to hydrate.

Eat where locals eat. Ask people for recommendations and specifically where they like to eat. You'll find really cool places that way.

Use trains to get around whenever you can! They're really great.

Scope out walking tours and big tourist destinations you'd want to hit. You may need to book a tour in advance to have any chance of seeing some sights.

Give yourself at least one rest day in each location where you can just walk around a cool part of the city if you want to or just hang out in a park or sleep if you need to. Many cities have very interesting, often very old neighborhoods with unique characters. For example, I would recommend checking out some Hutongs in Beijing.

Figure out your plans for sim cards and identification and such in advance. Plan out what apps you'll use and how you'll navigate them if you don't read Chinese. Many will have English modes but you'll need to find them and familiarize yourself with mistranslations.

You're not super super far away from Hakka walled villages for part of your trip. Could look into it as an option!

Have fun!