Terry, the business that is selling them in Australia may have an idea, but Easton.. or any other carbon manufacturer doesn't have a clue.. trust me on that. They know their compound stuff but when it comes to trad, they are in the dark. I have dealt with the guys at Gold Tip and also Easton extensively and most all decisions are made and designed purely on sales.
If you want to get him a bunch of arrows to last a long time, get the 1000's or 1200's. However with most youth, they go through arrows really fast. If you can get him just 6, I would get the 1400's and they would likely still be too stiff but that isn't really much of an issue. Then when he grows up a little, you can get him 6 arrows a little stiffer.
The tuning thing is very important to get broadheads to shoot well, but we have taken it too far in some situations. Unless your son is shooting with great form and consistency that is rarely seen out of most youth, he will never know the difference. the inspires are very small diameter putting them close to or at center shot. The bow will be able to handle a stiffer spine because of this. That and the total weight of the shaft .. it being very light are it's best attributes. If you go with a heavier arrow just so it can handle accessories, it will most certainly lose a ton of cast.
BigJim