Im shure someone will correct me if im weong but I think you can do that in the protox.xml file . first find the entry for house.
<unit id="465" name="House">then scroll down till you see
<buildlimit>10</buildlimit>this controls how many you can build
and
<populationcapaddition>10</populationcapaddition> ;this controls the population bonus for each house
hope this helps