With regards to UCMJ and Army [military] regulations, what are some golden rules for active duty service members owning store fronts?

I've gone down this road before, and the only rule you'll likely find (assuming USMC is the same as the Army) is the one requiring your Commander's approval for off-duty employment.

1SG (Join to see)
I've known a few members over the years who owned businesses, and what they did sometimes was list their spouse or a family member as owner or co-owner of the business. Nothing illegal, they did it mostly so that if the business were to do really well the military wouldn't try to discharge them for "being independently wealthy."

I would ensure your chain is fully informed and recommend seeking trial counsel so that they can provide you the appropriate resources. You are wanting to do the right thing and just need the info.
There are off duty employment rules, but they vary by installation. There are fraternization rules and you have to ensure you do not violate those. I have also heard about rules regarding the usage of government computers or resources for private businesses. Good luck.

Great advise from CPT Mark Gonzalez - Keep your chain of command informed. Just a side-note: Be careful how you enter into sales & contracts with your fellow service members. Once had a GySgt call me demanding to speak to one of my Marines. From the military side of the house, he had no business speaking to him... NONE. But, it was disclosed that my Marine defaulted on his line of credit to the GySgt's privately owned business. The GySgt was out of line to use his rank/position AND the DSN line to make collection calls for his business. So, his CoCO got a phone call, as well. We worked it out sans the legal department. But, both Marines had kind of made a mess.

Best of luck with your business, 1SG (Join to see)!

I am not aware of any laws,regulations, or rules barring a active duty service member from owning a store front.

Selling to your subordinates may be frowned upon

I never had that problem cross my desk. I have no idea where I get this memory, but I think the policy was: On a not to interfere with duties (normal or not) was ok for enlisted personnel. For Officers not, unless you are an absolutely silent partner, and never partnered with enlisted personnel.