Most especially at the start of your journey towards becoming the richest pirate, you will be easily acquiring enough gold to purchase upgrades to your island. Note that there is hardly any point in keeping all those gold coins idle so it is best to spend as much as you can on unlocking each island upgrade and progressing through to the next island. There are no hidden tactics on how you should spin the wheel of fortune, but fairly enough, you can be sure that the first 50 spins you make will earn you some shields to protect you against potential attackers.
With this strategy in mind, what you should be well aware of is the total money you have or can acquire as against the sum total value of purchases you can make to leave as little gold as you can leave in your possession. Ideally, you would go for purchasing the cheapest ones first with the mindset that you may be able to upgrade more features faster but in this game, what you would rather do is make a bit of advanced computations to ensure that your purchases result in you having only the amount of gold you can afford to lose.