thesniperdevil,
The point of this post is to show that the number of workers is a complicated issue and that the best approach to having enough workers depends on your goals.
The number of workers in a given city depends on the number of people living in non-scribal houses (residences and below) and on the ages of the residents. (There may also be a small random component, perhaps affected by scribal houses, but if there is then it only changes the number of workers by a few percent.) Only a fraction (perhaps 1/2) of the people in a certain age range (perhaps 11-49) work. The ages of immgrants may be randomly determined (within a specific distribution) when they settle in houses, but for a reasonable number of new immigrants in non-scribal houses the number of workers is generally somewhat over 40%. In my experience, this fraction may fall a little if there are a lot of births, but falls significantly after 15 or 20 years (due to retirement).
Near the start of each year, everyone ages 1 year, some people die, and new children are born. Some young people enter the work force. Some old people retire from the work force. Deaths are strongly affected by city health and appear to occur more in the old and (I'd guess) in the young. Births only occur when there are vacancies, but cannot fill too many overall vacancies or too many vacancies in a single house. (If a city has good enough health and no vacancies then only a small number of people will die and those vacancies will be filled by births. If a city has poor enough health then the number of deaths will exceed the number of births and the city will have more vacancies early in the year. If a city has lots of vacancies overall then births will fill only a small fraction of the vacancies.)
If you are trying to maximize the number of workers, then your best approach depends on what you are trying to do. If you will finish the mission within 10-15 years then you should minimize deaths and births. If you will run the city for a long time (more than, say, 20 or 25 years), then you should try to combat aging. For example (although I wouldn't do this except in a contest), you could regularly make lots of people leave by devolving some houses (perhaps by deleting their water supply) and then reevolving the houses and replacing the emigrants with new immigrants (who will have a larger fraction of young adults). Alternately, you could try to encourage births (by having lots of houses with vacancies as the city grows) and add new housing gradually (so there are plenty of young adults even when the city gets old). If you will run the city for a long time (such as hundreds of years) then you may have a problem with "ghosts" (people over 100 years old who disappear from the total population figure but still occupy space in houses, eat, and pay taxes).
Considering the type of worker house: you seem to be most concerned with having the most net workers per house (or perhaps per tile of housing). Why? If space is a limit then why not the most net workers per area? If a resource is a limit then why not the most net workers per a unit of that resource? If you tell us what you are trying to accomplish (and the problems you are having) then we'll be able to give you better advice.