I was curious about the low current as well.
If the fence is unloaded the current will be tiny. The only current flowing will be due to the leakage resistance, corona discharge and charging/discharging the fence's capacitance. The current should be much higher near the energiser than further away from it and will actually increase when a load is applied.
With capacitive coupling would you still recommend the 50v/2ma neon bulb??
The neons you've linked to don't strike until the voltage is at least 90V.
With the capacitive coupling arrangement, is gauge of wire important or just connected? I have anything from 24 gauge to 2 gauge cable available.
The gauge shouldn't matter as the current is very low. You could also try just connecting both leads of the neon to the fence and it may even light due to the corona discharge. If it doesn't light put a grounded metallic object (wire or even the fence pole) near the neon but too far away for an arc to from and it should light.
With the transformer arrangement would fewer turns and a heavier cable provide more current, low enough voltage to drive led?? I also have 16 gauge high voltage wire that I think is rated for 10 kv. I will have to look.
That's true but too fewer turns and the voltage will be too low for the transformer to act like a constant current source and drive the required burden resistor or LED.
Current transformers are used for monitoring high current sources but an electric fence is a low current source, try it if you like but I don't think it'll work, certainly not by inductive coupling, capacitive maybe. If you wrap several turns of HT cable around the fence wire and connect both ends to a neon and it lights then I think it'll be down capacitive coupling not inductive but if it works then so be it.