You didn't mention what state you are from. There are places where a homeowner is allowed to do work, including gas piping. There are places where this is absolutely fordidden. But in ALL CASES....EVERYWHERE.....gas work requires a permit. Your questions would indicate you may not have the skills necessary to do this work:
> Flex pipe is generally NOT used for gas work. There is a special coated stainless steel flex, but even to purchase it requires a training certificate.
> Flex pipe would not be used exposed to the elements, or to possible damage. It would not run through a concrete wall.
> There must be gas valve in the same room as the stove. Copper tubing is generally NOT used. The flexible appliance connectors are usually stainless steel.
> Connections to black gas pipe involve threading the pipe, and in the meter area, unions are often used. The union is connected to threaded pipe.