You are absolutely right; it’s very easy to get stuck with such!
And there is a cause for:
Too many people know too less of this quite wide field of science.
(I’m - still too!)
I will only talking about Aluminium!:
Why is it a wide field? There are nearly as much different kinds of coatings, - of course all made of Aluminium oxide -, as there are different recipes of the electrolyte in use!
Nearly all of these different coatings have also different features/qualities too!
As they have anyway some basics in common, a lot of your “answers” are correct but some “violate” other parts of your answers.
Correct is, that the natural (unanodized) coating is only of several nanometres, but its enough to protect for a whole life if the coating gets not injured. In case of mechanical injuries, the Aluminium repairs itself. But by mechanic-chemical attacks (Chlorides, Mercury for Example) there is mostly no real help possible anymore.
Some people tell you, that the anodized coating will be amorphous and porous (Wiki) and that such will give you the possibility to colour the coatings later.
As you may know, if it would be true, that the Aluminium would immediately “try” to repair such defects.
More correct is that the coating will follow “Epitaxy” rules, and that such is the cause why there is a strong “bonding” between metal and its oxide.
The “Pores” are in real channels inside the crystal structure and depends very strong with its diameters by the Electrolyte you use. These channels you can later fill with Pigments and close it by an additional process.
Quintessence: Corrosion-resistant is not direct correlated to the thickness of the coating, but this parameter makes it more robust to mechanical injuries.
The coating has anyway a Mohs hardness of 8-9, that’s why it is very abrasion-resistant (with the epitaxy)! That the oxide is a very good insulator with a high melting point is well known.
Finally, as both coatings are NOT porous and copper sulphate is not a strong etching reagent, nothing should happen with your drop, expect that it may dries up with time.
I hope it may be of help to you!
P.S.: If you prefer I can post a published model of a coating made in weak Sulphuric acid.