FOSS gamedev and creative worlds

Do waving water, waving leaves and waving plants decrease FPS? How much do these features "cost"?

No one can really answer that but you, it depends on so many other factors. Try it and see for yourself what your framerate is with and without those features enabled, then translate that into your own perception of 'cost'

Near open sea it should be more windy than within territory.

I just disable waving water, waving leaves, and waving plants as I believe they look completely ridiculous and cartoonish.

On the other note, I live in the midwest United States. It is windy nonstop every hour of every day here, sometimes gusts of 30 - 40mph. Yet, when I visit downtown Chicago which is right next to lake Michigan, there is a random light to moderate breeze off of the lake, but usually never continuous wild winds whipping every which way all day every day. So I cannot agree that open sea is windier than inland.

Not only can we predict framerates but now also the weather? <3