First off, I love seeing people follow their passion and don't want to deter an idea.
Second off, do not open a brick and mortar supplement store. Or a brick and mortar store in general.
I work in digital marketing, eCommerce and SEO and constantly have to keep up on industry news and trends. The moves that Amazon are making alone, will do away with brick and mortar stores alone. Not to mention what Google, Microsoft and Apple are doing either.
If anything can be done most cost effectively online, it'll only be a matter of time before it completely takes over. TV, brick and mortar stores, grocery stores, are all hemorrhaging money.
IF you are set on doing it, you would be better off creating a "boutique" type store, a place that creates an experience that'll make people want to come to you for their business because that cannot be replicated online. Trying to beat prices will not work because no company can compete with online prices.