On workers:
In my Tiny Chieftain game at 1000 BC I had 44 workers and 49 cities. By 510 BC I had 72 workers and about 94 cities. In my Small Regent game at 1000 BC I had 29 cities and 37 workers. 10 AD I had 141 workers and 162 cities.
Those numbers and my intuition tell me that you don't need, nor want all to many workers (unless you count the above as a lot of workers, which for the number of cities it doesn't seem like a high ratio). Irrigation only takes 4 turns anyways. The key lies in abstaining from building unnecessary roads. Only the 4/5 cities of your core should be fully roaded. Maybe you need roads to your border for transportation during a war. But, that's it! It's quicker to just irrigate and use the cities as roads. A city without a road can produce a worker as its first build. But, once it has a road and some irrigation, it can whip in a settler fairly quickly.