Age Of Empires/Civilizations/Rise Of Nations.

I am currently working on a map where each player starts out with a tribe of several tribes men in africa. You can then spread through out the world taking over cities. At the start of the game you wont pick races like AOE/Civ/RON. Instead capturing key cities gives you access to units/upgrades/traits. For example captureing cairo gives you accesses to chariot archers/camel breeding upgrade/and you get an extra +x gold every thiry seconds(the nile). While taking over Nanjing(A major city in china) would give you accesse to an early gunpowder unit,a research upgrade and a trait where every peasent trained gives you can extra one. I plan on making this map my self, but I need help on ideas and how to do things.
Things I need.
Races:
What races should be in the game. What shoudl their "Major Cities be" What Unit/Upgrade/traits should they get.
Cities:
I want each city to be able to only have 4 farms in it, each producing 4 food.
Only 1 Barracks per city.
Only 1 Temple/library/university/market/blacksmith... other buildings.
Any ideas on how to do this?
Resources: How should resources be gotten. I am basicly thinking of doing a city control way. Ex: Controling Nanjing would give you Y gold every Z seconds. Should there be multiple resources? If so what resources and how should they be repersented?
Units: Should all spearmen upgrade to pikemen right at the change from fuedal to castle age? Should the pikemen upgrade have to be reaserched first? Should spearmen never become pikemen? Should each induvial spearmen have to upgraded to spearmen?

Well it honors you that you are only asking for some idea feedback, while willing to make all the rest yourself.

I think your map shouldn't have too many races, because that will make the differences between every one seperately smaller. About 6-8 races should be fine.
You can easily steal some racial benefits/disadvantages from Age of Empires or so, or at least get some inspiration there.

I take it temples, barracks, and the like will be buildings on the map? So, basically, every city has a radius in which you are allowed to make buildings, and only one of every type?
I think a trigger like this should do what you want:

Events
A Unit is Issued an Order targeting a point
Conditions
Issued order is equal to (Order(humanbarracks))
Actions
* Check that it is allowed to build a barracks at the targeted point, e.g. check that the point is in the range of a city without a barracks.
* If player isn't allowed to make a barracks there, order triggering unit to stop and display "Not allowed to build barracks there".

This example would be for a human barracks only.. And maybe it would be bugged(if the triggering unit isnt stopped in time). So I should add some additional checks to also cancel/destroy all illegally constructing/constructed barracks, just to make sure.

I think you should stick to two resources, like gold and research or something, I dont know.

I think you should leave the old units as they are. Pikemen remain pikemen until they are killed/disbanded. But I don't think that matters much.. Just a personal opinion.