Not a dumb question at all! These days, we don’t add sand or anything. We have tried that in the past and it is a popular method. What I’d say is we didn’t really see “huge benefits” from it, and it’s a lot of extra work. Perhaps a slightly longer lifespan, but not markedly so. These days, we do a blanch and freeze (usually in December or so) of our extra potatoes into things like fries and hashbrowns, which greatly extends their lifespan.

With store bought potatoes, my guess is that flour or corn starch would provide no meaningful benefit. What you’re looking for are enzymes, which naturally occur in soil, that ward off disease. I would opt to just store them as-is. You can still get quite decent storage with the correct storage temperatures, just keep an eye on them. Since you don’t know how old they are, they may sprout earlier than expected. Shelf life is often reduced since they were harvested, stored, shipped and possibly sat at the grocer for some time. Good luck!