Praxden wrote:

It possible to have one trait that unlocks several techs or would each tech need its own trait or one trait that simply unlocks everything?

The line that unlocks the tech <Command Name="UnlockTechnology"Arguments="TechnologyDefinitionEmpireDevelopment2"/> 

Can be repeatedly placed in a single Faction trait unlocking as many different technologies as you want.

There is no limit (as far as I know) to the number of <command>s you put.

you just have to find the TechnologyDefinition name for each tech you want to unlock which can be found in the files %Install Folder%\Endless Space 2\Public\Simulation\ConstructibleElement_Science[Quadrant(Military/ScienceAndExploration/EmpireDevelopmentEconomyAndTrade)].xml

Just an example using my previous example. The Trait below would unlock 5 different technologies.

<FactionTrait Name="FactionTraitTechnologyDefinitionEmpireDevelopment2"SubCategory="FactionTrait"TraitCategory="TraitCategoryStartingTechnology" TraitSubCategory="FactionTraitTechnologyDefinitionEmpireDevelopment2"Family="FactionTraitFamilyStartingTechnologies" Hidden="false"Custom="true"Cost="10">
<Command Name="UnlockTechnology"Arguments="TechnologyDefinitionEmpireDevelopment2"/><Command Name="UnlockTechnology"Arguments="TechnologyDefinitionEconomyAndTrade21"/>
<Command Name="UnlockTechnology"Arguments="TechnologyDefinitionScienceAndExploration6"/>
<Command Name="UnlockTechnology"Arguments="TechnologyDefinitionMilitary32"/>
<Command Name="UnlockTechnology"Arguments="TechnologyDefinitionScienceAndExploration17"/>
<SimulationDescriptorReferenceName="FactionTraitTechnologyDefinitionEmpireDevelopment2"/>
</FactionTrait>