It depends on the laws of your state or country. I would say, to be safe, inspect the gas line and install the same type of fittings you find there.
Most codes do not allow Galvanized piping/fittings on gas piping. I have used galvanized pipe/fittings on exterior gas piping before in the state of Michigan but other states do not allows this. Check with your local code authorities.
Stenciling is used to identify the direction of flow and what the piping is used for such as fire supression ,gas , potable water ,etc
Brass is normally used for the gas connector to an appliance and for small shut off valves Piping and related fittings black steel is used ABOVE Ground in on piping not exposed to excessive moisture
No. You can use flared fittings with a flaring tool and soft copper pipe.
Piping material used for forming gas would be 316L stainless steel.
Compression fittings are used to join two tubes or pipes together. Typically it is used when the two pipes are different materials or different sizes. They are also sometimes used on pipes where it is difficult to solder or maybe dangerous to do so.
If you have a lot to install i would weld. 2 in. is a very big pipe to screw together
It is not a good idea to use copper pipe with natural gas as any sulphur compounds in the gas can cause an oxide to form in the copper pipe. Often copper is used with propane. In these instances, soft copper tubing is usually used with compression fittings. The tools required are, pipe cutter and 2 wrenches.
Check your local codes as some areas wont allow copper and require schedule 40 piping and fittings
No it will not poison you. Copper piping is used extensively in Medical Gas applications. "TYPE L" signifies the wall thickness of the piping.
If you are moving or adding on to gas pipes and fittings, it is highly recommended to get a gas permit. If there happens to be a failure on the additional piping your insurance will not cover it if your house blows up!
The purpose of a drip leg in the gas piping is used as a device to capture dirt and debris from entering the furnace.