I didn't go over it with a fine-tooth comb, but if your assumptions about potency are accurate, the rest of your reasoning looks sound.

Keep in mind that if you're going to use a large quantity low-potency material & then reducing it, you're going to be pulling a lot of unwanted stuff into the tincture & then concentrating it - it's probably really going to taste like hell.

I'm going to harvest a plant soon, & I plan to extract the fan leaves etc into butter or coconut oil, & then "wash" it several times - to deal with just that problem.