The post says I’m the boss, so as a human I’m going to pick my own home galaxy as the reference. Alien species would have their own coordinate systems but it’s not that hard to convert between them, or to specify which reference you’re using. We’ll already be converting between planetary/system/galactic/intergalactic coordinate systems all the time so it’s not much harder to account for a few more.
Somewhat but not exactly. You can only go north or south until you hit the poles, but you can travel forever at angle zero starting from the center point. I guess you could call towards the center point “North” and away from it “south”, so the galactic center is the North Pole but there is no equivalent South Pole. But angle zero is more analogous to the prime meridian - it’s a line that goes north-south but there are an infinite number of such lines, and we could have called any of them zero.