Specialist cities, universal improvements etc

Hi Im trying to teach myself to create specialist cities like all the big kids do. However I really can't stop myself from building the following improvements *everywhere* (and thus kind of inhibiting the myself in the process).

granary
marketplace
bank
university
observatory
aquaduct
barracks

I usually end up doing this because until later in the game my research is somewhat lackluster (I don't have specialist improvements to build), or I am landlocked and am waiting until a later age to wage a cross ocean war- so I don't have anything else to do.

Are specialist cities a late game idea?

also how do I effectively use specialists? Do I just spubtract worked city squares to stagnate a city once it hits ~size 20 and train specialists?

Does having specialist cities mean I should only cottage spam in my science and money cities?

whoops this is supposed to go in the civ 4 forum -_-