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
If the Find My iPad feature was enabled prior to it being “misplaced”, then if active, you would stand a good chance of locating it.
However, if the feature was not activated prior to being misplaced - or the iPad has been inactive for more than 24 hours, the last known location will not be available - and the opportunity to use technical means to recover the iPad have been lost.
As for your explicit questions…
Your iPad will only receive the pending erase command if, when it is turned-on, it has a network connection over which the erase command can reach the device. So, if yours is a WiFi+Cellular model of iPad - with an active Cellular plan - turning on the iPad within range of the cellular network should result in the erase command being received and executed.
If instead you have a WiFi Only iPad, it will only receive the erase command if it connects to a known WiFi network when it is turned-on; in practice, this is only likely to occur if the iPad can connect to a WiFi network that you have been using - as may be indeed be the case if the iPad is turned-on where you were last using it, as it is from here that the last known location was likely reported.
An iPad that is turned-off, or without an active network connection, cannot be commanded to erase.
As for gaining access to your data, whoever finds your iPad must know the iPad Passcode - without which the iPad cannot be unlocked. You only have a few opportunities to enter the correct passcode before the iPad will delay entry of a further attempt - each subsequent attempt causing an even longer delay before another attempt can be made. After ten incorrect attempts, the iPad will automatically become disabled - after which no further attempts can be made.
Your iPad has an encrypted file system. As long as the iPad remains locked, the locally stored data also remains encrypted. The encryption keys are stored within the iPad’s security chip (the Secure Enclave) - and only when the correct iPad Passcode has been entered to unlock the Secure Enclave are the encryption keys released to the Operating System. It follows therefore that without knowledge of the iPad Passcode, the encrypted data will remain protected.
As you now know, entry of an incorrect passcode will inhibit access to the iPad and its data. After ten bad attempts (which in practice will take many hours), the iPad will become disabled - at which point the iPad will automatically erase the Secure Enclave and the encryption keys; this process is known as a crypto-erase - after which any encrypted data stored on the iPad is permanently beyond reach and unrecoverable.
In summary, your iPad is designed to securely protect your data. As long as you were using a strong iPad Passcode known only to you, the risk of someone finding your iPad being able to access your data by correctly guessing your Passcode is very, very unlikely.
If you remain concerned, you might be well advised to change any critical passwords for banking, email and other important services. Naturally, you should report the loss/theft to the appropriate authorities.