Build right near the place where the immigrants arrive, in the following order:
Speed to 10%:
6x2 housing block with wells (houses 84)
work camp(across from housing, next to floodplain
4 farms on floodplain, as close as possible to camp
Speed to 60%:
firehouse, as soon as work camp is staffed.
granary, as soon as you have 12 extra workers.
architect, as soon as you have 5 extra.
When the flood came in June I had about 1200 units of food in the granary.
If the immigrants have to travel far, forget it. You need the work camp up and running in January.
An alternative -- 1200 units of flax, converted into linen and exported, could pay for importing lots of food, but only if you can export linen and import food by land. In Abu this requires an expensive trade route.
Perhaps two farming areas would do better. Who can store the most from the floodplain in year 1?