Good advice.
You can also burn a huge forest and rebuild some of the toxin scrubbers. Then you can plant some chunks of forest and put lots of greenery in between.
I found area III harder than area IV. After I got past the flowers, I failed the stage twice because I could not get the weather going. The steam generators need a 2x2 space of water with power and most of the good spots need some channels for the water and then you need to build power on top of that. This is really expensive on top of the already expensive steam engines.