Hi, yes gold filled is gold on the out side. Artistic wire comes in a lot of colors including silver. The same with Parawire. These are both copper wire that has a color coating on them. Copper wire is soft and is easy to use.
As you work the wire it becomes what is called work hardened. You can harden wire buy pulling it through a pair of nylon nosed pliers or after it is shaped you can harden it buy tapping with a chasing, leather, or nylon hammer on an anvil or steel block.
As far as wire used for ear wires I wouldn't go smaller than 20 gauge. I use 21 gauge 1/2 hard because it holds the shape better. I can make them very quickly so they don't work harden as much as I would like.
Wire used for clasps need to be a gauge that can hold shape with wear. A bracelet with heavy beads and/or stones would need a heavy gauge wire clasp. A dainty braclet with small crystals a 20 or 21 gauge can be used for a clasp.
The gauge of wire that you use for your spirals depends on the look that you want and how they are to be used. If you want a dainty look then use 20,21,22 gauge. If you want a more substacial look use 16, 17, 18 gauge.
I do suggest that you practice, practice, practice on cheapy wire first. Hardware stores sell copper wire for reasonable prices.
Memory wire is full hard and difficult to work with.
I hope that this helps you