No, this should not be a problem for visa processing.

Only additional documents recommended would be residence documents (lease or deed) and employment docs.

Yes you will need to disclose all and provide final disposition of incident. Consult with an attorney prior to filing.

Refer to your receipt for where the case is being processed and check the USCIS case processing webpage for specific guidance and timeline.

Best to consult with an attorney for guidance.

Unfortunately not until he is 21 and a visa would take 12-16 years to become available.

Upon departure you should withdraw the extension request.

If he can establish his intent then yes that is okay.

USCIS May be able to use previously captured biometrics.

Best to consult with an attorney for full review of Your case.