I’ll answer on behalf of Keith as i have had some experience with Asia Miles.
The term “easy” is relative. In frequent flyer world, I would say CX is one of the easier one’s to secure seat, especially all you are after is premium economy, and especially all you want is one way.But it won’t be freely available whenever you want it. It is nowhere like revenue ticket.
CX’s pattern is, usually they release a few (~4-8) seats at 12 months out. Then they are usually taken up by 9-10 months. Then about 14 days out, they release whatever unsold seats except one as reward seat. They do have a bit more seats to their own Asia Miles members. And it looks like they will reserve more seats for their own members rather than to partners. You can check the availability by logging onto CX’s website to have an idea of how easy it is to find the seats you want. You don;t need to have miles in your account to search.
As for your second question, whatever is available to QFF member is available to Asia Miles. So whatever QF flights you can see on Qantas classic award is bookable with Asia Miles.
Do bear in mind though, that one way award is slightly more expensive than 50% of roundtrip. So if possible, book roundtrip. Also note that whatever miles needed for redemption as shown on CX’s site is the minimal required for the itinerary, ie. for direct flights only. If your flight requires transit in another city (eg. SYD-HKG-NRT instead of SYD-NRT direct), the total miles needed will be higher than what is displayed.
Hope that answers your question.