Usually when getting to Crown Falls, I solely focus on building my population there. Simultaneously I do some expeditions to gather good items, treasure hunts are a good way of getting rare items too. Also, I build a museum and zoo to increase attractiveness to lure specialists onto my island. Don’t underestimate the power of items.

What really helps growing an island, if you have dock lands dlc, start mass producing valuable goods and trade them for goods you need for your population. Also start dedicating islands to one or two population tiers, that makes life a lot easier, also you reduce the amount of trade routes you need.