Here is Apple’s advice for lost or stolen devices:
If your iPhone, iPad or iPod touch is lost or stolen – Apple Support
Use the Find My app to locate a lost or stolen device – Apple Support
As for the security of your data, unless the iPad passcode is known, your data is safe. All iPad data is encrypted at rest; without the iPad Passcode, the encryption key that is needed to access your data remains locked-away in the iPad Secure Enclave (this being the iPad security chip) - the passcode being needed to unlock the Secure Enclave and release the encryption key.
If ten failed attempts to enter the iPad passcode occur, the iPad is disabled - and the encryption keys are automatically destroyed rendering data recovery from the iPad impossible.