Mainly it will be for hour building and navigation, but occasionally it will be used for 4 people for leaving the island
These may be two very different mission profiles. If you would like to fly four people and their bags several hundred miles, you'll need a 200+HP larger four place (a C172 really won't do this well). If you're content to bear the operating cost of that aircraft (40+ LPH of Avgas) for your hour building and navigation flights, no problem. However, these flights can be nicely flown with a 100HP+- power aircraft, which will operate for less than half the cost.
Consider buying low power, low cost, and renting when you occasionally need a hauler for four people.
Containering an aircraft across the Atlantic will cost at least $10,000, I've done it. It's doubtful that this added cost will make importing from North America attractive.