Question about MOSFET behavior
I'll just answer the NMOS part of your question. The answers for PMOS are similar, so the explanation should carry over.

a) Current flow through N-channel MOSFET transistor

Does not depend on V1's voltage
Depends on V2's voltage
Does not depend on the current charging the gate (from V2)


As long as you are operating the MOSFET in saturation, this is exactly what you expect. The relevant graph from the datasheet for your device is this:

When the gate-source voltage (in your schematic the voltage between N4 and N5) is high enough, only the gate-source voltage has a strong effect on the current through the MOSFET; the drain-source voltage (controlled by V1 in your circuit) has very little effect.
If you reduce V2 low enough, and by small enough steps, you should be able to trace out the roll off in the triode region, where both V1 and V2 will affect the current.

c) The current charging the gate is extremely low (about 0.0002fA).

This is exactly what you should see. The gate of the MOSFET is effectively a capacitor, and at DC will conduct almost no current.

b) Voltage across R3 is never higher than V2 - V1 (even if R3 resistance goes to infinity) &gt; and it doesn't depend on the V1's voltage.

Again this is roughly what you should see, but V2 - V1 is not the relevant parameter, the threshold Vgs of the FET is. If R3's value is increased at constant current, it will reduce the difference between N4 and N5 voltages. That is, it will reduce the gate-source voltage of the MOSFET, until  Vgs hits its &quot;threshold&quot; when the FET pretty much stops conducting altogether. So if R3 goes infinite, the MOSFET is shut off, and no current flows through R3. Despite R3 having a very high value, the voltage across R3 then becomes 0.