Can anyone give me a step-by-step on sea salt manufacture before the invention of plastics and heavy machinery? This is assuming a salt maker (salt-maker?) who's in close proximity to the ocean, in an arid seaside environment.
In Victoria (Australia) evaporative sea salt manufacture on a large scale was commenced in the 1880s by Richard Cheetham, so before the invention of plastics, although they did, over time develop heavy machinery for the task. Although they initially used gravity to move brine into the evaporation ponds or "condensors" and harvested and bagged the salt by hand, they later (by the 1920s) used electric pumps and designed a tracked scraper to harvest the salt. They also used a tramline to move the salt and machinery to raise it the big salt pile that was a landmark along the shore road. These salt pans were in use from the 1880s to 2007 and cover both the before and after details you are asking about.
Cheetham's also obtained other sites including one at Laverton, closer to Melbourne and most of your questions can be answered from the publication WORTH IT'S SALT: A Survey of the Natural and Cultural Heritage of Cheetham Saltworks, Laverton by Gary Vines and Brett Lane 1991.
For the site requirements such as sub soil composition, evaporation rates higher than rainfall rates and access to sea water see section "2.4 Salt Making Technology". Note that the sites in Victoria are not considered "arid" by Australian standards.
For the day to day details of how the salt was harvested see section "2.6 Operations at Laverton" which gives not just the step by step process but why the steps were taken, for instance including the brine concentrations required for different steps in the process which I note you asked about elsewhere.