Please see TIP: Understanding KM Variables, Tokens, & Functions
Variables vs Named Clipboards
In answer to your main question: "What would be better: Named clipboards, or Variables?"
==There is no reason, no advantage, to using Named Clipboards over Global Variables ==, UNLESS you need something other than plain text stored in KM Variables, like images, rich text, objects, etc.
I scanned, but did NOT read the remainder of your post: TL;DR.
If you have specific questions about using KM Global Variables , please post in a new, separate, and please be succinct.