I will be upgrading from 12.6 ASAP taking the precautions into account.
The INTL was causing me some concern but my webhost advised me that they could be turned on in the PHP settings and I have done that in readiness. The PHP info report that 12.6 provides no longer gives me the warning that INTL may be needed in future releases, so I presume I am ready in that aspect.
I haven't done any of a) or b) above and do not think going through the images will take much time.
Bring it on.