Salem

How can I achieve high purity for leather hides?

They take the purity from the Limed Hides.
Limed Hide purity is the average between the pelt and the milk of lime.
Milk of lime takes from the lime purity.

Is there high purity lime? Is there another way to produce leather hides without using milk of lime?

you can't because it doesn't matter at all

You can use rose otto to make rose-tanning-fluid which iirc takes only the % of the roses initially used to make the rose otto.

Yet again, there is no thing where the % of the leather would actually matter.

Does the purity of the Woo-Woo-Wand matter?

No