Well, Mikey, it sounds like you've surmounted issues 1 and 4 already! I'm not electrically competent enough to work out what gauge wire you might need, but I think that in terms of choosing a fine enough wire to look realistic, that may be an issue. Having said that, some of the wires used by Pola and Busch on their lights are very, very fine indeed. I did see an article discussing this in the US magazine Garden Railways recently, where the guy had worked out precisely what gauge wire was needed for each "leg" of the distribution network. It all looked a bit (over)complicated to me, I'm afraid. But I do think that a heavier gauge trunk run to carry the current required (and minimise voltage drop over distance), with thinner gauge local distribution wires might still be the way to go.
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