Don't forget New Guinea, Tekomandor. Just to give you an idea of how many people CAN live on New Guinea, take New Guinea and transpose it onto Colombia, so that the main mountain range is centered atop the Andes. On end drapes down to Ecuador and Northern Peru. On end curls onto Western Venezuela.
Now here are the population figures for those countries. Colombia 47 million. Venezuela 28 million. Ecuador 15 million. (I won't bother with Peru). We're looking at potentially 85 million people fitting comfortably in New Guinea alone. And a lot of lower Colombia is still rainforest.
Coffee growing in the highlands. Sugar in the lowlands. Multimillion person cities (Bogota", Quito at 9000 feet, (Mt. Hagen is at 8500 feet), Medellin at 5000 feet, Cali and Caracas at 3000 feet. Cartagena, Santa Marta, Maracaibo, Baramquilla, and Guayquil and Manta and Trujillo Peru at sea level.
Of course New Granada started being rebuilt from the 16th Century. But New Guinea starts out with well over a million industrious Papuans in the interior, who unlike Native Americans are resistant to European diseases. Once they are subdued, their population will start growing as an underclass. (Yes, a larger Australaisa will have an underclass). In fact they may be the key to settling the entire Top End. So find a way for Dampier's early exploration to lead to somebody climbing the mountains seen from Huon Gulf and exploring New Guinea's interior and finding the gold that's there. Plantations can come later.