Heaven help me - I've just bought a delta kit :-)

[curious aardvark]

just one zip tie, around a cooling fin, keeps the wires out of the way, and doesn't have a heat issue.

Ended up with similiar duct design to yours. But keeping the fan clip on top of the extruder carriage, that works a treat and once you've screwed the duct in place the whole thing is rigid while weighing about 4 grams.
You just need 2-4 screws holding the duct to the fan. And as I count spare computer screws by the lb, those i have :-)

Also going to have a seperate nozzle. That way i can play about with different designs without having to reprint an entire duct.

Actually, with your design you don't need the majority of that mounting plate.
If you just use the the two spare bolt holes, you can cut the mounting plate down by about 80% and still keep the same design. While not needeing to unbolt the extruder to change fans.
Hmm, now I'm thinking about doing that that instead lol
But you do still probably need to move the actual fan and cover onto the extruder platform.

Oh yeah, should you grab what looks like a mostly used roll of black pla off the shelf. Check it's not a sample of ninjatek's armadillo filament before printing a carriage with pla settings.
It almost worked too, but needed about another 30c printing temp I think :-)