Castaway Paradise

This is not to be confused with the second story of your house. There are two upgrades available for your house but only the first one is needed for this trophy. To unlock it, you will need 15,500 coins to build up your house.
 

Making Money

The fastest way to earn coins in the game is through Fruit/Trees. The Acai Berry, Chestnut, Juniper Berry, Orange, Peach and Cherry all sell for 3125 coins each. As soon as you can, you want to start planting any of those, and a lot of them.

If you can plant 10-15 trees in a line, you can essentially bank anywhere between 31,250 and 46,875 coins an hour. Along side that, if you happen to level up at any point, the trees will auto complete the growing cycle, allowing you to harvest Fruit much quicker than a per hour basis. Harvesting the trees alongside doing quests will bank you many more coins than any other task available on the island.

The more trees you plant, the more coins you will make. By the time the game was complete, I had 51 Acai trees profiting just under 160,000 each harvest.