Well, we will have calendar and could just go into improving the tile anyway. If the build was worker => settler (Asymptote/Cape) => settler (4th city) then the worker has time for a plantation and chops before that fourth city.
So I'm still a little uncertain, and I'd be willing to just switch to the settler if we really want the overseas city faster. The worker is a bit better in the long term though, especially with tech going so fast. One chop, into the plantation next, and then going to road/farm for Singularity (Singularity pushed back to fourth or fifth city though), seems like it could work. The chop does serve a pretty solid purpose of speeding up that settler which we are concerned about.
Regarding iron - I don't really see how that becomes necessarily apparent to other civilizations - if we start building swords, sure, but it won't be a major change on military stat otherwise. Anyway, they will see that we have the actual tech Iron Working since we have Alphabet and the F4 tech screen. But I do agree we could hold off for building more warriors, and might not be working the specific mine improvement right away yet either.