"BuffStackingLimitType" determines whether the stack limit is "PerPlayer" or "ForAllPlayers", for example if i set the stacking limit to 1 "ForAllPlayers" then it really will only stack once, however if i set it to 1 "PerPlayer" then each player will be able to apply 1 instance of the buff.

"PrioritizeOldBuffs" means that it keeps the oldest instance(s) of the buff when reapplying, so if I have a 30 second long buff and 10 seconds in it gets reapplied it will just ignore it and keep counting down from the original buff. For a buff with 2 for the stacking limit it would keep the first two instances and ignore any further instances, etc etc

"PrioritizeNewBuffs" means that it will remove the oldest instance of the buff when reapplying, so in the previous example the 30 second buff being reapplied after 10 seconds would go back to having 30 seconds, and again for the buff with 2 for the stacking limit the first two would apply as normal but then any further buffs would overwrite the oldest of the buffs.  

EDIT: Well thats how I think it all works...

Additionally, my best guess for buffExclusivityForAIType is that it helps determines whether the AI Players will attempt to use the ability that applies the buff on something which already has the buff.