Well, if you're planning on depicting an Australia-sized area, I'd aim for just one or two plates. Too many, and it becomes really implausible (technically, you'd want to figure things out on a planetary scale, if you really plan to do the tectonics in-depth). Many of the lower mountain ranges can be explained by either volcanism or as old ranges that are the result of older collisions (the Urals, Appalachians, and many others). This means that you don't need (or even want, necessarily), an active tectonic boundary for each mountain range. However, in the place where you want the highest mountains in the world (the west-east oriented range in the middle?), you would need an active tectonic boundary.
So, basically you'd have a continent formed by two converging plates. The rest I'd drop, it's a good idea to keep it simple if you're not doing the tectonics in detail. It's worth noting that there aren't any (major) plates that consist of only continental crust. They typically have a leading edge of continental crust, with a trail of oceanic crust formed at a mid-oceanic ridge. So, two continental plates colliding sounds perfectly plausible. Then you need to decide which plate is being subducted. If you look at the Himalayas, for example, all the mountains are formed on the side of the Eurasian plate, whereas you have an area of lowland on the side of the plate being subducted (the Indian plate, in this case). So, generally speaking you'd expect the topography on the side of the subducting plate to be much higher in comparison to the topography of the plate that is being subducted.
Another thing worth noting is that a subduction zone (and therefore, the mountains formed via subduction) have a strong tendency to form a convex curve (convex on the subducting side). Again, the Himalayas is a good example. This is because it's less work to subduct a plate in this fashion. However, the other side of the coin is that if a concave subduction zone is present, you'd expect the highest peaks to appear there (like the Altiplano in South America), precisely because concave subduction takes more force and causes a greater degree of deformation as a result.
Here's a very quick and ugly draft of how (I think) the tectonics that explain the present topography should look (of course, this is just a very quickly drawn suggestion, nothing authoritative, feel free to use, modify or to ignore):
Kronos Tectonic Draft.jpg
Here, purple represents a convergent continent-continent boundary, blue is a subduction zone (where oceanic crust is being subducted), and green is a transform boundary (the plates moving sideways). The arrows are drawn on the upthrown side (the subducting side, in other words). The orange lines are there to highlight old mountain ranges that are the result of past collisions/volcanism (and as a result should be relatively low and eroded, like the Scandes or the Urals, for example). If you decide to use this suggestion (or something similar), it's worth noting that there would probably be some island arcs appearing along the oceanic subduction zones (the blue boundaries), on the upthrown side.
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