There is a lot here, so I'll pick a couple.
A tungsten light bulb is non-linear, but resistive. In fact the resistance is about 10x lower at startup. It's just the Resistance-temp coef of Tungsten.
DC component.
You may be missing something. In a push-pull amplifier like audio is usually class A-B. In Class A-B, there is a slight conduction of one of the transistors at all times. That's not the same as offset either, and it's called a DC bias current. When there is no conduction at all, the amp experiences cross over distortion. The Vbe drop of the output transistors vary with temperature and that's the job of the bias regulator.
DC offset usually results from the lack of matched components. If you have a high current output, transistors are paralleled. When they are paralleled a small emitter resistor is used to equalize the current. The gains of the transistors have to me matched as well.
I'd still call it crossover distortion or something like "crossover delay" or "crossover time". It is usually a time where both push pull drivers are turned off. I probably would not call it a "DC component".
High/Low Z
An ideal voltage source has Zero resistance
An ideal current source has infinate impeadance.
Thevinin and Norton's theorems.
Check them out:
https://en.wikipedia.org/wiki/Norton_theorem That's one of them.
It basically says that a voltage source can be replaced by a current source in parallel with a resistor and a current source can be replace by a voltage source in series with a resistor. These are very important concepts.
An audio amplifier uses the term "damping factor" to denote a varient of Z. An amp that is designed for 8 ohms with a damping factor >100 has an output Z < 8/100 ohms.
In other cases the change in V divided by the change in I can be called the output impedance.