1) Nothing about the area where the new businesses are being built/was fought over during the turf war. The further into the sub-levels one goes, though, the more intense the emotional state of the plants will be, whatever that is.

2) It is, for the most part, the circulatory system of the city. The soul energy that regulates the city's power is run through there, extracted from the waters of the sanzu and used to power the generators in the lower levels.

3) They would think of the celestials as people that tend to take things for granted, which leads to...

4) ... Mostly they would like the Lost Souls to not do that.