You got everything already covered quite well. Steam Power is with no doubt the most powerful, and MrRandomGuy already started on it, good. Industrialization for factories and Scientific Method for Theory of Evolution are also top priorities. Let me add a third one: Replaceable Parts. The doubled worker speed is
huge!
Using the free techs from ToE for getting Hoover's Dam is also very strong. We could even start two pre-builds, one for 600s and one for 800s, so that the Hoover Dam can be finsihed right in the same turn where we reach Scientific Method...
In a recent Spaceship succession game we did the following: we delayed ToE right until the end of the Industrial Age, so that it would complete in the same turn as our last industrial tech. We then took two very expensive modern age techs as our freebies: Computer and Miniaturization. And we had another prebuild for 1000s finishing on the same turn, which we then switched to the Internet. So we got the huge science boost from the Internet right on the first turn of the modern age! (And managed to finish the remaining techs in 4 turns.)
However, that game was only Monarch and we were able to keep the AIs backward by draining all their cash for some out-dated techs. I don't think we can pull this trick off in an Emperor game: the AI would probably finish ToE, before we are able to research the last IA tech...
So taking the Hoover Dam is probably the better choice here.
choxorn is right: pollution will not be a big problem in this game. Just consider the following. Pollution is caused by 4 factors:
- If a city becomes a metropolis (size 13 and up), the population causes pollution.
- Factories
- Coal Plants
- Manufacturing Plants
In my experience, pollution only becomes a pain in the neck, if 3 of these factors coincide. E.g. in a recent game I had metropolises at size 16-22 with factories and coal plants and they polluted like 2-3 tiles per turn.
In our game, however, we won't have time for researching Sanitation, so all cities stay at size 12, we won't have Coal Plants because of Hoover Dam and I never build Manufacturing Plants, because they come so late in the tech tree, that they would not even finish before the space ship launches... (Robotics is the most expensive tech in the game and therefore gets researched last. At that point of time all space ship parts are either already built or the prebuild is already collecting shields, so wouldn't be able to benefit from a Manufactoring Plant anyway.)
So out of the 4 points, only factories will be causing pollution, and that is so neglectible, that it doesn't really matter. Probably in the range of 1 polluted tile every 5 turns or so.
In the industrial age the AI has three very strong research preferences: Nationalism, Communism and Industrialization. (In that order, I think.) In any case, they are just crazy for Nationalism, so as we got that as our freebie, I recommend to gift it to everyone (except England of course...

) Once we get Steam Power, we gift that to the stronger AIs as well. Then we have a slight chance that while we do Electricity, Replaceble Parts, Medicine and Scientific Method, two of the stronger AIs will do the unavoidable Communism and then Industrialization. (Once we see Communism available somewhere, we should try and trade for it and then gift it around as well, so that no other AI wastes any more beakers into it...)
It is quite unlucky that we lost Korea, but with a bit of planning, we might still get the AI to do Industrialization and another one of the upper branch techs for us. On Emperor the AI is not that bad...
And to answer your question of what to do with the "excess food" once we have rails on our food tiles: we turn it into shields!

For every irrigated tile that gets a rail, we can change another irrigation into mine - for an additional two shields!
Example: currently a grassland tile provides 3 food, 0 shields. If we have two of them, we rail both and build a mine on one of them. This changes the tiles from "3.0 + 3.0" to "4.0 + 2.2" ==> Food output remains the same, but we get an additional 2 shields.
So the order of worker tasks in the core should be something like this:
- If we haven't grown all core towns to size 12 by then (and don't have enough workers for joining, which I think will be the case, because rails are now more important), we rail the irrigated tiles of the small cities, so they can finally reach their target size quickly. (Three rails usually bring every city to +5 food and a new citizen every 4 turns.)
- Then rail the mined plains and grasslands. (In the cities that can make good use of the extra production.)
- Then rail the irrigated plains, floodplains and grasslands of the big cities (and mine half of these tiles)
- Then rail the hills.
- And finally the mountains.
(I think this task list shows you, why Replaceable Parts is so important...

) Of course this list may need to be modified according to strategic needs, e.g we should also strive for getting a connected rail link from our core to the British front to improve our war effort, once the war is restarted.