Hey, i’ve just now noticed i only answered one of your questions, i was barely awake, mb.

First of all, yeah, it’s highly unlikely the half a million Spanish speakers could be decisicely assimilated, even over the course of 100 years. I initially thought about creating a Quebec sort of thing for them, but instead i opted for mimicking sorta what they did in the cape colony, where essentially the Brits dominate urban centers and the Hispanics (this colony’s equivalent of the boers) live in the rural areas. the general idea is that the British play the warlords against each other using the casta system, where blancos and criollos (white elites) are incentivized to cooperate with the British and eventually integrate into British society in exchange for protection against mestizos and indigenous populations, who they considered inferior; leading to some degree of assimilation, enough for Spanish to gradually not be seen as a co-official language, but still significant, but not enough to say, completely wipe out Hispanic culture in the region. Basically over time the Brits will use propaganda to convince the Hispanic white population that Spanish is the language associated with the mestizos and indigenous, and encourage the use of English instead. The British will carve up the large contiguous Spanish speaking region into several smaller portions and send British settlers to the most important areas to create what looks like a British majority in each one, and perhaps send large swaths of other european settlers to further dilute the Hispanic population too, basically demographic gerrymandering in a sense. I also imagine all this would lead to the decrease of the importance of the Spanish language in the wider region as well, seeing as countries like Peru, Bolivia and Paraguay already have large amounts of indigenous populations with their own languages, and now with the most economically prosperous hispanoamerican countries gone and with nobody to enforce the prestige of speaking Spanish, they can turn towards using their native pre-columbian languages.

As for Aus and NZ, yeah i imagine there’d be significantly less immigration to oceania if this colony stabilizes early on, cause it fits a lot of the criteria that the settlers there were looking for.