see my comment on step 3 that this should be done earlier.
These instructions are correct that you don't want to overtighten, the throat of the heatbreak is fragile and you can twist it right off if you apply force with a tool.
BUT when the whole thing heats up the heatsink seems to expand more than the heatbreak and it can become loose in use which you really don't want. So it needs to be firm at this point, but not tight enough to risk damaging anything.
A suggestion I have seen and support although I haven't tried it yet myself is to get the heatsink warm with a heatgun or hair dryer before screwing in the heatbreak, then it should grip better when it cools. I imagine it doesn't actually need to get very hot, since the heatsink should never be hot in use.
confirmed - it should read 2mm
I would strongly recommend using M3 machine bolts instead of self tappers. IMO proper bolts and a threaded heatsink to accept them should be standard. The fan blocks the bearing bolt, so you can’t disassemble it with the fan on, so every single time you need to do anything to your aero (other than adjust the idler tension) you will have to remove the fan.
when adjusting the body rotation for backlash be aware that you are also moving the hole in the centre of the heatsink relative to the motor shaft, which could cause it to rub, causing excessive friction. I actually lightly reamed the heatsink hole with a drill bit and lubricated it with pencil graphite. Not sure if that was really necessary, best just to make sure the motor shaft doesn't touch the heatsink at this point.
these instructions - steps 3-5 - don’t really work on an Aero since they lock the heater block to the heatbreak, and therefore also to the heatsink in a fixed and arbitrary rotation . If your final heater block orientation matters to you then you need to screw the heatbreak into the heatsink first. I wrote a more detailed explanation but it’s too long to post here.