Well it's the old story, shop around, buyer beware etc.
Quite frankly you need to really do your homework on every aspect of purchasing a vehicle overseas & importing it. Plus you need to get to know the 'Mustang world' really well if you're not already an informed car buff.
Personally, in your situation, I'd be looking at buying a car already compliant, registered & on the road here in Australia, plus with at least a certain amount of known history, receipts, photos of work done, etc.
Yes you may be lucky & buy well in the US & get it over here & on the road & save a bundle, but the potential - & more likely - also is to really come a gutser & end up with a major money pit & on-going headaches. There are plenty of horror stories. Plenty of scamsters around.
So go to car shows, meet Mustang Club members, get to know the cars, see what's around, get familiar with the scene; car people are friendly & love to talk about their cars. And if you don't immediately see some cars that turn your head, take your time, don't rush it. And you could take a look at whatever's available through this forum's advertisers too, on the RHS of the page.
Be very careful with 'kitted' cars like that Eleanor-styled car you tabled, a kit can easily hide all sorts of bodged-up stuff. Like rust - Mustangs can be shockers - & crash damage. The K$15 tag seems way too cheap too, red flag there.
But that aside, welcome to the Mustang world if you're planning to join us!