You probably should have asked this in the "Dunnunda" forums, maybe a mod can move it there?
The answer is: a PPL or above can fly a factory built LSA with transponder (up to date RAD43/47, of course!) into CTA without any questions asked. Happens all the time here.
Yes, go for RA-Aus, it'll save you a bundle in maintenance and if your son wants to learn to fly in RA-Aus, he wouldn't be able to do that in a VH registered aircraft.