1st. Yes, you've omittted to do many required things in Modbuddy. All you've done so far is added the files to the project, but you haven't told ModBuddy what to do with the files you've added to the project.
see whowards tutorial on
what to do with the .dds files
You need to do OnModActivated > Update Database > FileName for your xml files.
(note that as shown in whoward's tutorial ElsaScene.xml is an exception to this rule)
Issues in the Files themselves:
Happiness is not a yield, and therefore does not go in the <Building_YieldChanges>. Eliminate that whole <Row> --- </Row>
Code:
<Building_YieldChanges>
<Row>
<BuildingType>BUILDING_WANDERING_OAKENS</BuildingType>
<YieldType>[COLOR="Red"]YIELD_HAPPINESS[/COLOR]</YieldType>
<Yield>2</Yield>
</Row>
<Row>
<BuildingType>BUILDING_WANDERING_OAKENS</BuildingType>
<YieldType>YIELD_GOLD</YieldType>
<Yield>1</Yield>
</Row>
</Building_YieldChanges>
Instead, use this (the blue text)
However, see where I made your text show green? This does work but it's generally better to use a TXT_KEY_BUILDING_XXX reference instead, and then fill-in the actual text you want to show in-game within the <Language_en_US> table.
The structure of these three might tend to clash.
<FreeBuilding>BUILDING_SNOW_QUEEN</FreeBuilding> in the Trait is giving the building to all cities anyway, so the extra insurance you've got in the <Civilization_FreeBuildingClasses> isn't adding anything for you. Also, since the game generally only wants to give the class of building specified in the <Civilization_FreeBuildingClasses> table to the capital city, this is where the potential clash might arise.
Code:
<BuildingClasses>
<Row>
<Type>BUILDINGCLASS_SNOW_QUEEN</Type>
<DefaultBuilding>BUILDING_SNOW_QUEEN</DefaultBuilding>
<Description>TXT_KEY_SNOW_QUEEN</Description>
</Row>
</BuildingClasses>
<GameData>
<Traits>
<Row>
<Type>TRAIT_ELSA</Type>
<Description>TXT_KEY_TRAIT_ELSA</Description>
<ShortDescription>TXT_KEY_TRAIT_ELSA_SHORT</ShortDescription>
<FreeBuilding>BUILDING_SNOW_QUEEN</FreeBuilding>
</Row>
</Traits>
</GameData>
<Civilization_FreeBuildingClasses>
<Row>
<CivilizationType>CIVILIZATION_ARENDELLE</CivilizationType>
<BuildingClassType>BUILDINGCLASS_PALACE</BuildingClassType>
</Row>
<Row>
<CivilizationType>CIVILIZATION_ARENDELLE</CivilizationType>
<BuildingClassType>BUILDINGCLASS_SNOW_QUEEN</BuildingClassType>
</Row>
</Civilization_FreeBuildingClasses>
Unless I've missed it I don't see where you are defining this:
Code:
<Unit_FreePromotions>
<Row>
<UnitType>UNIT_ARENDELLE_SNOWLEM</UnitType>
[COLOR="Red"]<PromotionType>PROMOTION_SNOW_LIFE</PromotionType>[/COLOR]
</Row>
</Unit_FreePromotions>
Not sure if you have any other errors or potential conflicts.