nvm figured it out that I have to put my mod files in the ..\Documents\My Games\Elemental\Units\ directory

Have you succesfully altered the population limit?

I've been trying but my alteration is adding to the default and i can't figure out why.

My intended effect is to have to build more housing structures to raise a city's level.

I've been experimenting with raising the population requirements for tier increases (as well as lowering how much population a city square holds) and lowering the population provided by housing.

EDIT: I can get around the fact that the two values combine by making my modifier value a negative. That works OK for the city pops but for housing it makes the infocard look ridiculous (if my file has a -15 modifier to population then the infocard shows that the structure houses +25 -15 people)

Yep, those are the two values. I can get the city level population working satisfactorily but i wasn't happy with the idea that both xmls were combining values. It just didn't seem to be the way it should work...

As to balancing, it's going to be a pain because the food bonuses will need tweaking too hehe.

My initial aim with changing the housing populations was that i was contemplating adding more tiers of housing. I'm also going to remove (if possible) the auto upgrading of huts into houses upon a research breakthrough. I want to have to decide to replace structures to increase capacity

I intend to do similar things with ALL bonus structures so that i really have to specialize. For example, if i want enough food to feed an empire then i want to have to dedicate a city to it with many granaries to store the food.

On the combining values thing, it's weird.

in K_CityHubss.xml,  under the "outpost" section it has this for the initial population capacity of the tile;

        <GameModifier InternalName="Storage_Population">
            <ModType>ResourceStorage</ModType>
            <Attribute>Population</Attribute>
            <Value>10.0</Value>
            <Cumulative>true</Cumulative>
        </GameModifier>

If i make my own xml and set this to 1, when you place a city, the initial population capacity will be 11 because it's added my 1 to the original's 10.

Now the section for the level limit;

        <GameModifier InternalName="LevelOne_LevelCap">
            <ModType>LevelBarrier</ModType>
            <Attribute>Population</Attribute>
            <Value>25.0</Value>
            <CityUpgrade>Village</CityUpgrade>
        </GameModifier>

but if i change that to 50 in my own xml, the city WILL only require the 50 i've set.

I really don't get why the Building Tile Limit was their solution to players just spamming houses to reach stuff. Why not just limit the number of houses a player can build to eight, or make them require more upkeep past a certain point?

Sure, put this file into your "Units" directory (Mods should work too).

ModCityHubs.XML

NOTE: This is a test version. I'm currently trying to imeplement some kind of a tax system and the ability for minor civ's cities to grow (needs testing).

Perhaps your placing the modification in your "Data" directory?