STORY OF SEASONS: Friends of Mineral Town

The horse derby money making method is mentioned in several places online, but because I prefer to read it over watching a video I found this site most helpful: https://guides.magicgameworld.com/story-of-seasons-friends-o...
I found 3 methods that can work, so pick the one that works for you :)
Horse Derby is held Spring 18/Autumn 18
You will need:
Biggest rucksack (Completely empty for all the dresses you will buy)
As much money as you can get
4 hearts or more with Huang (to unlock selling option)
Horse race starts at 10am, so do your morning chores and SAVE before walking into Rose Plaza, so you can reload and not have to do your chores each time.

A lot of people say bid on the horse with the highest odds, and keep reloading till they win. I think that is fine if you are doing this early on and don't have a lot of money. I tried this method and wasted over an hour with the same 2 horses winning every time.

If you have over $100K, just bid as much as you can on the winning horse. The winning horse usually swaps between 2 horses, so pick the one with slightly better payout (10+ odds hopefully) and reload till they win. The odds will stay the same each time on the first race, but not the 2nd and 3rd. You will make your money back easily and then some.

Third method I found is enter the race yourself, on your first couple derby's you will have very high odds on your own horse, and you can bid on yourself, plus have an effect on winning the race. Bid max amount on yourself on the 3rd race and reload till you win.

Once you have your medals, first buy the Gem of Truth and Power Berry. Then buy as many dresses as you can fit in your backpack. The next time consuming part is selling each dress individually to Huang, he will buy them for 11,700 ~ 12,700G each.

~Now my experience was a bit different, because I did not look into this method till my 3rd year. I was very successful with bidding on myself and getting a load of medals, but I did not bid max amount or know to buy dresses. After reading about this method, I ended up bidding on a horse with 10+ odds, did the max 9999 medals which costs over $400k. I filled my inventory with dresses, sold them to Huang and made about $2.5 million. I would have to wait till the next derby to fill my inventory again with dresses and unlock this achievement. This will need to be spread out over a couple derby's because you can't hold enough dresses to get the $5 million in one derby. I had to fill my inventory twice with all dresses to get the $5 million, but it will pop while you are selling Huang :)

Good luck and I hope this helps!