An update from the sellers had me (mostly) convinced I'm worrying unduly.
The items that had shown as not shipped had been shipped but the seller had not updated eBay
The item that appeared to be coming from China instead of Sydney is, my seller assures me, shipping from China. The message I received about Customs delays in China was a standard message sent to all purchasers.
As there's no tracking, there's no way to confirm any of this. I guess some times you just have to trust people .
