Hello,
01. Sale/Discount functionality comes from WooCommerce end and the Theme directly doesn’t influence it. For the Variable Products, the Sale Label shows the Percentage for the highest defined Discount on the available Variants and doesn’t change with the variation selection. You can confirm this from one of our Test Site products too.
https://blackpearlspro.com/woodmart_support/product/augue-adipiscing-euismod/
This above Product has the highest Discount percentage of 45% and it is showing that as Label on the Product. This is how it works
02. Navigate to Products > Attributes > Edit Attribute and choose the swatches size.
Please check this:
https://xtemos.com/docs-topic/variable-products-and-swatches/
03. Sorry, but there is no option available for that in Theme Settings.
It requires customizations and this is beyond our limitations and support policy.
Best Regards