Regarding the "when to build the worker" issue, always remember that when comparing hammers/commerce of the different options, you have to take into account how long the worker needs to improve tiles, and that we need to utilize Pottery ASAP by constructing early cottages (or we shouldn't have researched it in the first place).
However, before we can construct cottages, we need to improve the other tiles first! Early cottages might give the capital an early science boost, but mid-term we need to build units and settlers to expand. For this, the extra commerce will not help - we need food and hammers instead.
So we want to irrigate the rice and mine the two hills first at least before we start to construct cottages on the floodplains, so that when our capital has reached its maximum size we can stop its growth and have max hammers for units, or max food+hammers for settlers. I always forget the exact number of turns these improvements need, but including worker movement, irrigation plus two mines will take at least 15 turns or so.
Now if we wait too long with building the worker, for example by letting the city grow to size 4 first, we will have wasted our early Pottery research! Instead, we should have researched something that would have been useful immediately, like BW to see where copper is. But since we have gone for Pottery already, we need to utilize it, which means we need an early worker.
In conclusion, I strongly suggest to start building the worker as soon as the warrior has been finished. In single player games, I would have even built the worker right out of the gate, but I guess in a multiplayer environment that is too risky.
-Kylearan