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1 - Depends on the fitting. If it's a bayonet, one pin is live, one is neutral. As I understand it, it shouldn't matter. Just make sure if you use a single pole switch, you switch on the line (although the one below is double pole, IE switches line and neutral).
2 - 3amp would be fine, I=P/V, so if it's a 50w bulb, it'll only need 0.2A of current.
3 - This looks nice/vintage https://edisonlightglobes.com/Shop/shop/hardware/plugs-and-switches/black-10a-inline-switch-240v-2/Also, if it has a metal case/exposed metal bits, I'd probably add an earth.
I've got an old lamp with two wires that needs a plug. Ie no earth.
Questions:
Cheers