"Południu" is locative form of "Południe"= noon/South
Yes. To me as a native Polish person, those concepts are inherently the same.
Wschód(East) is where słońce wschodzi (sun rises)
Zachód (West) is where słońce zachodzi (sun sets)
Południe (South) is where sun is at południe (noon)
I imagine północ (North) as a direction where sun never is , but I guess you can also imagine sun going full circle - half at day (above), and half at night (below), and północ=North is where in this imaginary journey sun would be in the middle of the night. (midnight=północ)