Thats a lot of questions lol. Sorry about Twitter, bit of a noob on there. + social media over load.
Steam release will be identical for the moment with the itch update being a week behind the launch as i have to put all my effort on that, depending on how well it sells more features and Steamworks will be added. You are better off waiting for steam than buy it here, because from my understanding by reading Valves TOS i cant give keys to a competitor store front selling the game for cheaper, and also requesting keys for 7k users might not be possible as it states in the guidelines, that up to 500 key requests is reasonable, beyond that i dont know, ive asked them, but have not had a reply yet. FlowScape has been built primarily with user requests for the past 6 months, and if enough people buy it to sustain further development, that will continue.
As for your other questions, this is a one man dev team, so you may be disappointed by the amount of no's you are about to get :)
3. no this is a diorama creation game, not really a playable game
4. lake yes, rain yes, thunder lighting yes, sounds yes, wind yes, rustling yes.
5. No cycle but you can set your own day or night or dusk scene by applying the appropriate settings
7. no cycles, just settings to achieve said environments
8. summer at the moment but am experimenting with winter right now.
11. if you create the largest terrain and paint at the smallest scale, its 1 km. but you can bring your own objects in to make bigger terrains.
Hope that helps, there are a lot of videos on youtube, go check them out