As others have said, the most important item is airspeed. Too fast will cause many problems:
- Over controlling is more likely (particularly in pitch) as the controls are more sensitive
- Everything happens faster
- You have too much energy (speed) going into the flare, which means that ballooning is more likely and will be worse, e.g. at 75 knots too much back pressure might take you back up to 10 feet when at 65 knots it might have been 2 feet.
- If you are trimmed for 75 knots instead of 65 you will need more back pressure for the flare, making fine control more difficult.
- You spend more time in the flare waiting for the speed to bleed off, which amplifies the effect of any gust, error etc.
- You are more likely to land nosewheel first due to the flatter approach attitude and extra back pressure required in the flare.
On final, you need to set the speed
first, then fine tune the aim point. Changing speed will change the aim point anyway.
If you are being taught 60-65 knots on final that is good - from memory that is about right. I would suggest you aim to be stable at 65 knots by 300 feet. The earlier you slow down the easier it will be.
I would suggest:
After turning final, set power and flaps and use back pressure to slow the aircraft to 65 knots, then trim off most of the pressure. As the aircraft slows you might look like you are overshooting, but that is OK - you fine tune that
after the speed is stable.
Once you have the speed at 60-65 knots, adjust power to keep the aim point stationary in the windscreen. As you change power forward or back pressure may be required to keep the speed stable (quite likely forward pressure when increasing power, back pressure when reducing it). Trim off any constant pressure.
The aim is to set up a stable descent ending at the runway, so that the aircraft almost goes there by itself, rather than needing to "drive" it to the runway.
The exact height you turn final is not so important - the final approach will be influenced as much by wind anyway. Of course consistency is better but 550-700 feet sounds OK especially if you have a long final approach, as I suspect is the case at Moorabbin.
Again, the key is to be at the right speed, and build everything else on that.
As for the centreline, once you are in the flare the aim is obviously to touch down travelling parallel to it, but it is too late to make major adjustments left or right. Aim for the centreline through the approach, and if you are far enough away from it at flare height that you are in danger of running off the runway go around.
In the flare use the rudder to keep the nose pointed down the runway (the same as you do taking off) and aileron to stop drift left or right and keep the aircraft travelling parallel to the centreline.
Hope this helps.