Die polishing lines should only be on the fields, and the lines are raised, unlike cleaning hairlines or whizzing. The straight lines on that Three Cent
piece cross onto the devices, so not die polishing lines, but they might be planchet striations. They are too linear to be whizzing.
I agree almost completely with this.
My only possible disagreement could be with the last statement.
"Planchet striations" are very possibly the source of the straight lines since this coin:
-- the metal is nickel alloy and the Mint was having difficulties early on getting full strikes on that metal hence "planchet striations" often remained.
Whizzing is one form of cleaning and was often done with a soft polishing wheel. A wire brush would be an extreme case.
The high speed used during whizzing often creates enough heat to melt a thin layer of a coin's surface and move the melted material to the side in the direction of rotation.
But with the nickel alloy that is unlikely.
The answer to 5) is a definite "yes".