Great questions. I have been playing since 2013 and have the love shack, which MAYBE lets me make one alicorn a year. I have max of everything, all level 5. For energy I have 2 wizard schools, Queen's keep, barracks, and haunted keep. I have 14 weekly alicorns and 16 weekly ones. I have $64 mill. i was maed on almost everything at the start of this quest. I have 2 kitchens and 2 winter bakeries, Ivy's bakery, food shelter, bountiful table, mystery dinner table, and I just bought a second harvest pergola. i have 3 red trilium, 2 multi-colored hedge, 3 faerie flowerbeds (I bought 1 with gems.) and I flower garden. I haven't bought much with gems, and I get a lot of gems through quests. Is the barracks still available for you? That would be my first choice. Also get haunted keep if you can; I do not know what is available.
When they have an event, they often have something for gems that just works during the event (like a plant to drop petals). I avoid those.
I have finished and have the peacock, but this was very time and energy intense. People shoudn't have to set a timer every 2 hours for 20 days!
Good luck!