Do not bring your normal personal devices to China. They are notorious for injecting spyware on foreign devices at every opportunity. Use a freshly formatted device and create all new accounts to use with it.
Regarding services: do not use self-hosted services unless you you spin up fresh, isolated instances of your services for use while abroad and spin them down afterwards, including formatting any OS they were hosted on.
Regarding VPN: because we are assuming that any device used in China is compromised, do not connect to your VPN unless you have set up a segregated VLAN and are connecting through a VPN server instance created specifically for use while in China.
Basically, assume anything you use in China is compromised. And assume your connections are being monitored. And assume that any device you are connecting to from China is at risk of being compromised. So everything needs to be segregated from the rest of your network and set up specifically to be deleted after you’re back home.
Unfortunately, no, not really. They are absolutely able and willing to confiscate your devices at any time once you’re on Chinese soil, and once you’ve lost physical control, that’s the end of trust for that device. Even beyond that, it’s not unheard of for there to be vulnerabilities in Wi-Fi, Bluetooth, etc that make your device susceptible to wireless attacks. IMO it’s not worth the risk.
Here is just one example of this type of thing uncovered by The Guardian, New York Times, and others in a joint investigation: https://www.theguardian.com/world/2019/jul/02/chinese-border-guards-surveillance-app-tourists-phones