Safe in that it cannot physically harm you, otherwise, no.

That depends what you mean by “safe”.

You should expect that any WeChat account can be accessed & controlled by China government.

Most modern mobile operating systems have permission control, meaning it can’t just access everything on your phone. Access to your files, photos, camera, mic, location, and etc. can be controlled by your phone’s settings. However, there are things that cannot be controlled. Many sensors do no require special permissions to access, orientation, gyroscope, accelerometer. Device ID like imei and serial numbers may be accessible, depending on your os. Now I’ve never heard of Wechat having malicious code, but if it does, it could gain unauthorized access to your device data. Apps stores tend to not allow malware on their platforms so the Google Play and Apple Appstore versions are probably not malware, but it can become spyware if you grant it enough permissions.

Edit: Also, Wechat requires internet access to work, so any data you input can be accessible to the company. Now Wechat is owned by Tencent, a Chinese company. China is infamous for requiring companies to share data with the government. So everything you send through the app can be assumed to be in the hands of the government of China

Card info no, why would it, they have their own payment systems over there, and your credit is of no interest to them.

Contacts, yes if you allow it.

It’s no worse than installing Facebook.

Use a backup phone that’s had all its data reset.

If you don’t feel comfortable using it, talk to your coworkers about your concern and see what they think, and ask them if they are more comfortable switching to something else for work.

Your enemy’s enemy is your friend. It’s “safe” as it will not try to steal your crenditials. Although it is a privacy nightmare itself but think as people in China wouldn’t care much about Google’s privacy policy as noone will use the information against them.

Wishing you luck on your journey to finding a secure messenger app! You’ve been searching today, lol. Have you tried Matrix?