ETA: The Deluxe Soil does not vanish on Ginger Island - whatever fertilizer you put in, stays indefinitely, so it's just a one-time expense.
In my experience, it won't run out if you plant a re-harvesting crop on Deluxe Retaining Soil. But if you put a single-harvest crop on it, it runs out the moment you harvest the crop. I could
very well be wrong, and it could be that I play on Switch, so I don't have the numerous fixes/improvements that 1.5.5 brought. I'd just make sure with a quick test before you plant hundreds of Starfruit!
But to answer the question, I feel like a greenhouse full of Ancient Fruit is enough money to supply all your needs in the long term, especially if you're not super high on friendship and other requirements for
Perfection. And your time is precious, so plant re-harvestable crops because they require less effort. Plant some Coffee to keep your legs pumping, plant some Corn, Eggplants and Tomatoes for all your culinary needs, plant some Pineapple because Pineapple!
Fruit Trees will harvest every day; you can buy Taro Tubers for two Bone Fragments each at the Island Trader (when you unlock it, if you haven't already) so you don't even have to leave the Island for seeds. Hot Peppers are great for Pepper Poppers!
But there are also some surprising don't-s: Don't place Scarecrows, you don't need them on the Island (and there is no need to scare the lovely parrots), don't hope for Giant Crops (they can't appear on Ginger Island), and don't forget to leave paths so you can walk through your beautiful farmland.
Hope this helps, have fun!