If your community has a zoning law that requires stores to not sell alcohol, explicit material, guns, etc, within a specified distance of a school, your city council representative or your zoning department would know that. If they are in violation, then you can request that your councilman address the issue through proper channels. But most of the time when a charter or independent school is located in an empty business building, businesses that were previously there are grandfathered in and not required to relocate just because the school moved there.
A gun shop in and of itself wouldn't worry me nearly as much as a bar, a liquor store, or an adult video shop. Most of your seedier types are not going to go the legal route for a gun, so you'll likely find a lot of people who are trained and respect firearms.
But you have to live with your comfort level, and that is different for each individual,
