why the R7.6 at the outer axle holders?
at R7.5 it could be easily done with 3x ring1 and 1.5x ring4 (without the quads)
should the outer corners of the "tread" be rounded (torus prims)?

The quad+ering solution is better as it uses less vertices than the 2 x ring prims one.
Edge of wheel is as sharp as other Duplo brick corners, so no need for tori.

Found a better image, maybe the torus is worth modeling on front after all
https://www.steinpalast.eu/media/image/70/c2/6e/2131h9wcix4JzWFNo.jpg
Maybe also the middle front dimple, though probably a simple molding artifact, would be worth modeling, as it's pretty visible.

I would also go for the middle dimple it is very prominent, ut just a simple injection point

Origin should be in the wheel.

The wheel width is 2.5 mm = 6.25 LDU, the outer diameter is 17.0 mm, and the diameter of the flat surface is 16.0 mm. That leaves 0.5 mm or 1.25 LDU for the tori. A 1 LDU tori is overkill. If something is really really needed, the corners can be rounded with a simple 1 LDU cone.

The injection point is smaller than on most Duplos and the docs clearly state that injection points shall not be modeled. I know rare exceptions have been made, but those have been much larger and way more prominent than this.

The R7.6 is slightly rounded from the physical radius of 7.625 LDU. Further rounding to 7.5 or 8 is possible, but I didn't see the benefit.

Moved origin to surface of wheel as requested.

should the orientation match the standard "rotation axis is z-axis"?
would mean to rotate it and rotate it back in the axle assembly, like here:
https://library.ldraw.org/parts/15703

Will rotate. Is there any standardized nomenclature for wheels?

Rotated wheel as suggested

Wheel nomenclature:
https://forums.ldraw.org/thread-7479-post-7482.html?highlight=wheel+nomenclature#pid7482
It all started there.

I often use this as a reference:
0 // Wheel (solid)
0 // Nomenclature: width_(mm) x diameter_outer_(mm) [optional qualifier]
0 // 2470.dat "Wheel 2.8 x 27 with 8 Spokes"

0 // Wheel rim
0 // Nomenclature: width_(mm) x rim_diameter_(mm) [optional qualifier]
0 // 11208.dat "Wheel Rim 10 x 14 with Fake Bolts and 6 Spokes"

0 // Tyre
0 // Nomenclature: width_(mm)/ profile_as_%age_of_width x rim_diameter_(mm) [optional qualifier]
0 // 18977.dat "Tyre 11.2/ 28 x 17.6 Intermediate"

0 // Wheel Rim and Tyre (assembly shortcut)
0 // 2903c01.dat "Wheel Rim 14 x 62 Motorcycle with Tyre 17/ 70 x 62 Motorcycle Offroad"

0 // Wheel and Tyre (dual moulded, non removable)
0 // 39367p01.dat "Wheel 14 x 48 with 4 Spokes with Integral Medium Azure Tyre"

Added outer curvature as suggested. Added central bump as suggested. All purely for esthetics.