Nano refers to the diameter of the coil itself. So you can have a nano quad coil if you wanted. Nano is usually defined as anything lower than 1mm in diameter (I think this is right, some people define them differently)
I don't think there is something defined as a regular sized coil, but a micro is usually around 2mm in diameter as
coils larger than that are usually called mini
coils.
Not every micro or mini coil is a touching wrap coil either, although most people do use this as part of the definition.
Confused yet? Yeah, me too.
As for the kanthal, I have 26, 28, 30 and 32 on hand. I enjoy experimenting. If you were only going to pick one gauge, 30 is a pretty versatile type to use. Just remember that when building dual coils your final resistance will be half of the total resistance of both the coils. You should always use and understand Ohms law if you have any doubts.
Finally, if you are new to rebuilding, remember to be safe and know the limits of your battery and vape within those limits. Also have a way to check resistance of your coil before mounting and firing.
