Thanks for starting this! I'll be glad to contribute what I know (or believe). Hopefully we can use the tail of this thread as a bit of a scratch space for the moment and then Canarsie can come back and delete the posts where we were discussing and improving the initial posts.
Quick morning thoughts/corrections: AZ often requires a long sell. The statement on YQ/IOS is less than ideal. I'd suggest rewording as follows:
• DL the past few years has been increasing two sneaky and notorious fees often blurred as a tax. First is the carrier-imposed YQ or YR surcharge, which is often labelled as a fuel surcharge. The amount is generally based on the amount of YQ/YR that the operating carrier would charge on a revenue ticket in the given class of service when the ticket is sold with a US origin. DL collects the YQ/YR surcharge on many of its partners at this point. However, DL, AF, KL, and AZ metal will not result in YQ/YR collection except if you originate in Europe. This is often referred to as the International Origination Surcharge. It does not apply for tickets originating outside of Europe on DL metal. In addition to Europe, tickets originating in the Middle East and involving travel on AF or KL (and maybe AZ) will invoke the IOS. Note that the IOS is simply just a rebranding of the YQ/YR surcharge. It will be coded on your ticket receipt as YQ and/or YR. The best way to estimate your fees/taxes is to build a paid ticket with your itinerary on ITA and check the fare breakdown.
I'll work up some instructions on ITA, since, for instance, there are some taxes that won't be charged on YQ-free tickets and it's important to use a US place of issue to get accurate YQ/YR charges.
For the VA section, please change to Virgin Australia (to avoid confusion with VS and VX). The best search method is the Velocity Rewards site. Sign up with any random Australian address and then search for their cheapest awards. Those should be available to DL, but it's important to note that you should not search one-ways. Search round trip originating in the US, as more inventory is made available to Velocity Rewards members for Australian origins. This inventory is reliably bookable on delta.com, but the award calendar will not show it.