Some changes I play with to have a more fun game:

RESOURCE LIMIT and OVER COLONIZATION
C:\Program Files (x86)\Steam\steamapps\common\Endless Space 2\Public\Simulation\SimulationDescriptors[Empire].xml

<Property Name="MaximumStrategicStock" BaseValue="999"/> and change it to 9999
<Property Name="MaximumLuxuryStock" BaseValue="999"/> and change that to 9999
<Property Name="AllLuxuriesStock" BaseValue="0" MinValue="0" MaxValue="17982"/> and change that to 179982

In the same file, for largest map size search for GalaxySizeGigantic (last one, GalaxySize of 7) and change OverColonizationThreshold value 14 to something much larger like 30


BIGGER and DENSER GALAXY
C:\Program Files (x86)\Steam\steamapps\common\Endless Space 2\Public\Settings\WorldSettingDefinitions.xml

To get a bigger and denser galaxy, search for Gigantic and try these values:
<KeyValuePair Key="NodesQuantity">140</KeyValuePair>
<KeyValuePair Key="IsolatedNodesQuantity">38</KeyValuePair>
<KeyValuePair Key="SizeScale">1.25</KeyValuePair>
<KeyValuePair Key="MinorFactionsCount">12</KeyValuePair>

Then search for GalaxyDensity and in the High section try these values:
<KeyValuePair Key="GalaxyDensityStatus">1.50</KeyValuePair>


SMALLER INFLUENCE BORDER
C:\Program Files (x86)\Steam\steamapps\common\Endless Space 2\Public\Simulation\SimulationDescriptors[ColonizedStarSystem].xml

SystemInfluenceRadius value for Power change from 0.4 to 0.3. Do the same for SystemNextInfluenceRadiusEstimation