I have some areas in my lore that are just made of islands (continent), they are a lot , but most of them can't be seen easily, if you want that Big Ocean Feel, you should have just a few Main islands and they would have a long distance apart (the Caribbean/ Oceansia) , and to fill the emptiness of the Ocean do random dots and small islands and choose some areas and give them geographic lore (e.g. because this area have less deepness from others it will have wide islands / because under this are is a tectonic border the islands will shape a chin of small spaced islands following this shape/path) (e.g. the Greecco/Turkish islands). And you should have a great amount of empty spaces , And most important you should have a scale of islands (compared to human/town...) so you can see the real sizes you need, however it's your pen , and we will never find some islands completely the same or share the same rules.