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.