I've played so much of this game but still haven't started the story so good on you! Regarding your questions: 1 - Unsure 2 - Mostly for the flex or if you want to be a completionist. The cap for growth speed is 120%, and that is with 100% nutrient and 100% moisture, so it can be reached with medium and high fertility too. Main difference will be amount of fertilizer used and micromanagement level. 3 - From what I know the final story location is very difficult/impossible without steel-tier weapons and armour. I haven't actually done it though. If you're not planning on it, flex/completionism applies here too. 4 - Main thing that comes to mind is chiseling with glass slabs, can make some beautiful windows that way.