SC2Mapster

I've not used "Target Finds" and "Target Sorts" so I don't know how they work (just try out changing something and see how it works, I always do this).

Judging by name "AIThinkInfestor" is "Tactical AI Function" - a function from standard triggers library. Trigger functions is used for some units that has many castable abilities or require more difficult logic than simple autocast. You can write your own tactical AI function and set that field to the "script identifier" of that function (function real name in compiled galaxy script). Example AI Think Function (from "Mutators COOP" lib, "Heroes From The Storm" mutator):

CT_AmonHeroTychus_AIThink
    Options: Action
    Return Type: (None)
    Parameters
        ------- All AI Think Triggers Must Have the following three parameters, no more no less
        Owner = 0 <Integer>
        AIUnit = No Unit <Unit>
        NearByUnits = (Empty unit group) <Unit Group>
    Grammar Text: CT_AmonHeroTychus_AIThink(Owner,AIUnit,NearByUnits)
    Hint Text: (None)
    Custom Script Code
    Local Variables
        Target = No Point <Point>
        AbilityRange = 0.0 <Real>
        AbilityDamage = 0 <Integer>
        AbilityAoE = 0.0 <Real>
        ------- Comment
        Score = 0 <Integer>
        ------- Comment
        OrderVariable = No Order <Order>
    Actions
        General -If (Conditions) then do (Actions) else do (Actions)
            If
                Or
                    Conditions
                        (Number of Living units in NearByUnits) <= 0
                        ((((Mutator Amon Tychus Toss Grenade, 0))) is valid for AIUnit) == False
                        (Cooldown of cooldown Abil/MutatorAmonTychusTossGrenade on ability Mutator Amon Tychus Toss Grenade on unit AIUnit) > 0.0
                        (AIUnit order list has an order with ability Mutator Amon Tychus Toss Grenade) == True
            Then
                General -Skip remaining actions
            Else
        ------- Comment
        Variable -Set AbilityRange = (Value of Abilities MutatorAmonTychusTossGrenade Range[0] for player Owner as an integer)
        Variable -Set AbilityDamage = (Value of Effects MutatorAmonTychusTossGrenadeDamage Amount for player Owner as an integer)
        Variable -Set AbilityAoE = (Real((Value of Effects MutatorAmonTychusTossGrenadeDamage AreaArray[0].Radius for player Any Player)))
        Variable -Set Score = 1
        ------- Score is tallied per unit potentially hit, 1 point for Vitality >= Damage, otherwise (Vitality/Damage) points 
        Variable -Set Target = (Returns the best location to place and AOE attack on the group with the specified parameters ((Units in NearByUnits having alliance Enemy with Owner, with at most Any Amount), 3, AbilityDamage, Score, AbilityAoE, (Position of AIUnit), AbilityRange, c_unitAttributeNone))
        ------- Comment
        General -If (Conditions) then do (Actions) else do (Actions)
            If
                Target != No Point
            Then
                AI -Suggests order ( Toss Shredder Grenade (Tychus) targeting Target) to AIUnit using tactical AI logic
                General -Skip remaining actions
            Else

This "Tactical AI" is like AI-only ability autocast. In data editor they are under "Advanced Game Data" - "Tactical AI Data" tab.

I think sharing power source is a default behavior for alliance. Stetmann power field behavior have different "Power Link" than the one created by Pylons, so you can't build using Stetmann's power field without Pylons, unless you change that "Power Link" field to match the one set for Pylons.

If you are talking about units not getting buffs from Stetmann field: first you need to make sure that unit has "Coop Controller - AllUnitBehaviorController (Unnamed)" behavior - this one setup all behaviors needed for coop unit (like having unity barrier (Karax) or shield regen when cloaked (Vorazun)) this include buffs from Stetmann's fields. You also may need to run other Coop-related triggers to make all this buffs work.

About alliances: there is a trigger "Set Alliance", "Alliance Setting: Ally With Shared Vision and Pushable" should do the trick. There is also "Set Alliance Aspect", that have "Alliance Aspect: Shared Power".

There is a filed in data editor on zerg units "AI: Tactica AI" - removing value from this field should disable burrow/unburrow. There is also "Enable/Disable Script Control For Unit" trigger (and same for unit group): "If script control is enabled for a unit, the AI will not use that unit.".

I couldn't find one, but you can do it like this:

pick each (all units that can be a magazine ammo units in entire map) - if (Magazine owner of picked unit is what you need) then ...

In data editor search "playerdecal". You need to change 3 actors: for terrans it's "Command Player Decal W", for zerg - "Hatchery Player Decal1", for protoss - "Nexus Player Decal W". In field "(None): Visible To + " set "All" to Enabled. Hint says "When on, prevents the actor from being seen by anyone".

What offsets you used for addon? Y = -2.5 and x = 6.5 ?