100% Requirements are: -All 10 Power Berries -All 7 Event Photos -All 18 Fish -All 27 Bugs -All Plant Photos for the gender you're using -All Farm Extensions -Good Ending
The Farm Extensions cost a total of 180k g in the run, but you can get 30k for free by winning the Horse Races. You could trade a chicken to another cartridge and back again to make it golden, which sell for 10k g each, but that's banned, iirc. We don't know the exact reqs. for the Good Ending, but I'm looking into it. If it has anything to do with GBC 1 & 3, it's most likely Happiness / # of Shipments / A few of each animal / Power Berries.
Edit: Good Ending reqs. are 10,000 total shipments, all 10 power berries, 70 happiness, 3 of each animal.