The patch notes indicate which stages have received changes in which modes:
http://nintendoeverything.com/splatoon-version-2-0-0-full-patch-notes/
a) Nobody has written up a description of exactly what the changes are too my knowledge, but that would be difficult in some cases as for example Underpass is basically a completely different stage, and the bottom of Moray Towers on Splat Zones is also way different.
b) Not out of the weapons that launched with the update, but I imagine if you main aerospray you're more likely to like the Slosher than the Splatling.
c) To early to tell really, but based on Azure's lobby last night 2 Sloshers + Tentatek + Dual Squelcher looks to be super effective for splat zones, at least on warehouse.