Is there an official Google Apps package? So I understand that I need to flash the gapps package after installing a custom Android distro (ROM). In that case, is there an official google apps package? If so, why should I rely on competing distributions of the Google apps package, rather than get it straight from Google? If not, do device manufacturers get it through a different, private route?

If not, is there any way I can extract the Google Apps platform whole from my own device's stock Android OS image? As I understand, that is in fact the exception which Google allowed, which everyone seems to be abusing by simply distributing APKs extracted from other devices. I have not seen a single guide for this.
Official GApps package is never available publicly. Google only provides it to authenticated OEMs like Samsung and HTC. It'll be installed only on Google Play Verified devices, in their stock ROMs.

That's why individuals can only download and flash unofficial GApps packages.

You can, of course, extract Google Apps from an authenticated phone and install it elsewhere, but you'll surely do extra job in comparison to flashing well-prepared packages.