It says "Increase tradeable goods" "-1% Population Growth"
You can even test. Start new campaign. Add money then add pop to rome to 24. then process_cq up to cities then you will see its -500 before its build then -2400 after its build.
no positive affect anywhere else. after that building is build your economy TANKS especially the more of them that are built in different cities. you can always destory it but that means you have to manager every city so it doesnt get rebuild.
sorry. as to your other question its a progress build. suburbs then town then.. cities (TANK) No money for legions oops LOL