Oracling into Metal Casting then building colossus is always out there. We wouldn't be the only ones trying it though. I dare say approximately 5 other teams would be going for the same thing. There's no particular reason we couldn't win such a race, but large sacrifices would certainly have to be made.
Consider that we're probably not looking at long spindly islands here like the AI makes for archipelago maps and really lend themselves to the colossus. This is a stunty round island where cities will all be coastal, but still have a large amount of land available to them. In general, it's still better to work cottages than coast I think, even with colossus.
To me, stonehenge was about the charismatic trait more than the border pops and it isn't continent limited. You'll want to have monuments everywhere anyway, so it's just a question of whether it is better to build stonehenge or individual monuments, which I guess comes down to how many cities will get built early. I'm not really sure how new information about the starting location changes that decision. It may be that waiting to get boats online and then explore a little before we build a 4th city means we have the time to build stonehenge without costing much. Or it may be that the couple of strong city spots we have early on means that we can knock those monuments out quick then down the line when cities on the other island get lots of support it's not a big deal to put up monuments there either.
Based on what we see here, I think it is highly likely that all the other teams are on an island of similar size with many instances of a single food resource, a single hunting or mining happiness resource, and a single calendar resource. Stone and marble, if they are to be found, are probably on that other island we see. It may be that everyone sees that other island the same way we do and that the fight for world domination takes place over there. Or it may be that island is just another stepping stone.
P.S. This probably changes things enough that we could come up with some alternate plans and vote on them.