Actually it might not be plentysector.
Just tried it out with nexerelin, dynasector, ss+, and a ton of faction mods and it worked perfectly.
EDIT: Some weird **** is going on. Started a new game as interstellar imperium with templars enabled, but templars are not in the faction list on intel screen.
EDIT2: Started new game as hegemony and got the templar crash.
Spoiler
601041 [Thread-4] ERROR com.fs.starfarer.combat.CombatMain - java.lang.RuntimeException: Spec of class [com.fs.starfarer.loading.K] with id [tem_templarmarket] not found
java.lang.RuntimeException: Spec of class [com.fs.starfarer.loading.K] with id [tem_templarmarket] not found
at com.fs.starfarer.loading.SpecStore.o00000(Unknown Source)
at com.fs.starfarer.campaign.econ.Submarket.readResolve(Unknown Source)
at com.fs.starfarer.campaign.econ.Submarket.<init>(Unknown Source)
at com.fs.starfarer.campaign.econ.Market.addSubmarket(Unknown Source)
at exerelin.world.ExerelinMarketSetup.addMarketToEntity(ExerelinMarketSetup.java:580)
at exerelin.world.ExerelinSectorGen.populateSector(ExerelinSectorGen.java:1109)
at exerelin.world.ExerelinSectorGen.generate(ExerelinSectorGen.java:782)
at com.fs.starfarer.campaign.save.CampaignGameManager.super(Unknown Source)
at com.fs.starfarer.title.TitleScreenState.dialogDismissed(Unknown Source)
at com.fs.starfarer.ui.M.dismiss(Unknown Source)
at com.fs.starfarer.ui.impl.I.dismiss(Unknown Source)
at com.fs.starfarer.campaign.save.if.actionPerformed(Unknown Source)
at com.fs.starfarer.ui.h.o00000(Unknown Source)
at com.fs.starfarer.ui.OooO.processInput(Unknown Source)
at com.fs.starfarer.ui.h.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.ui.ifnew.dispatchEventsToChildren(Unknown Source)
at com.fs.starfarer.ui.ifnew.processInputImpl(Unknown Source)
at com.fs.starfarer.coreui.intsuper.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.ui.ifnew.dispatchEventsToChildren(Unknown Source)
at com.fs.starfarer.ui.ifnew.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.O0OO.oooOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.ui.ifnew.dispatchEventsToChildren(Unknown Source)
at com.fs.starfarer.ui.ifnew.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.M.processInputImpl(Unknown Source)
at com.fs.starfarer.campaign.save.if.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.ui.ifnew.dispatchEventsToChildren(Unknown Source)
at com.fs.starfarer.ui.ifnew.processInputImpl(Unknown Source)
at com.fs.starfarer.ui.P.processInput(Unknown Source)
at com.fs.starfarer.title.TitleScreenState.processInput(Unknown Source)
at com.fs.starfarer.BaseGameState.traverse(Unknown Source)
at com.fs.state.AppDriver.begin(Unknown Source)
at com.fs.starfarer.combat.CombatMain.main(Unknown Source)
at com.fs.starfarer.StarfarerLauncher$1.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
EDIT 3: Turns out nexerelin creates a new market called tem_templarmarket in ExerelinMarketSetup.java, which must be causing the crash. Not sure why it crashes though
Edit 4: Also turns out templars have a custom submarket named tem_templarmarket. Still not sure about what is causing the crash.
Edit 5: Found something. tem_templarmarket is coded to be a MilitarySubmarketPlugin, but plentysector causes markets to be extended as PlentysectorMilitarySubmarketPlugin. Two different types of market plugins. Still not sure why it crashes though.
Based on the line in the crash report:
at exerelin.world.ExerelinMarketSetup.addMarketToEntity(ExerelinMarketSetup.java:580)
I'd say the crash happens when nexerelin executes this line:
newMarket.addSubmarket("tem_templarmarket");
Edit 6:
So apparently the crash report is saying that there is no such thing as "tem_templarmarket"
Spec of class [com.fs.starfarer.loading.K] with id [tem_templarmarket] not found
Since there is no specId (the type of the templar market) with name "tem_templarmarket", so this is null and you cannot do myMarket.addSubmarket(NULL) ... Which leads to the question,
why is it null?