Technically this is OOC information, but I feel that it's needed information to make the most of the Harmonization vote which is why I am posting it. Note that these values are subject change if I consider them too powerful or underpowered when they end up being merged.
Every 5 styles merged stacks the applicable values by 1, the cost of merging styles increases the more you merge in bulk or merging more styles into already merged styles. It is cheaper to merge many together at once than it is to do so piecemeal.
All stacking options are given a value at which they cap.
Ultramarines: Unlocked
Non Stacking Aspects
Extra Actions: +1 action to advisors
Stacking Aspects (5)
Improved effects of legal actions
-50 to Infrastructure DCs, applies at 5x to Megaprojects and Radiant actions
Dark Angels: Can be gained via Dark Angel successor chapters
Stacking Aspects (5)
+1 stage to counter intelligence level that does not cost upkeep and applies to finding important people
Raven Guard: Can be gained via Raven Guard successor chapters
Stacking Aspects (5)
+1 stage to spies
reduces action DCs for infiltration and spycraft by 50
Iron Hands: Can be gained via Iron Hand successor chapters that follow the culture of the original chapter
Non Stacking Aspects
Improved Ad Mech relations
Better Ad Mech diplomacy
Stacking Aspects (5)
Reduces Research DCs by 50
Imperial Fist: Can be gained via Imperial Fist successor chapters
Non Stacking Aspects
Upscales defense quality by a Tier to a cap of High Primarch
Prevents wounds from being taken during fallback to preplaced defensive lines
Stacking Aspects (5)
-50 DC to Defensive actions
-50 to the cost of building complex defenses
Kin (Squats): can be gained via diplomacy with the Kin
Non Stacking Aspects
Increases tier of orbital bombardment required to impact defenses
Stacking Aspects (5)
Increases Defenses wound totals by 2
Increases mining action caps by 5
Martian: Unlocked
Non Stacking Aspects
Machine Spirits are more resistant to scrapcode
Provides 0.05 to the system Extraction and Production bonus
Stacking Aspects (5)
Education +1
Tech Priests of Magos or higher gain +5 to their focused field
White Scars: can be gained via White Scar successor chapters
Non Stacking Aspects
Willpower training is 10% more effective
Stacking Aspects (5)
Psykers gain 1 tier of willpower
Humans gain half a tier of willpower rounded down
Space Wolves: can be gained via the Space Wolves
Non Stacking Aspects
Enables all military forces to punch up by one tier of quality, caps at Peak Solar Aux
Astartes act as if they are a tier higher, caps at Low Primarch
Stacking Aspects (5)
Unlocks melee specialization training for military forces
Improves military training
Aeldar: can be gained via diplomacy with the Aeldari
Non Stacking Aspects
Champions start at Tier 3 in their focus
Heroes start at Tier 5 in their focus
Legends start at Tier 7 in their focus
Stacking Aspects (5)
Psykers skills are increased by 1 Tier, caps at Astarte novice
Psyker willpower is increased by 2 Tiers, caps at Tier 6
Necron: Shezu would be willing to provide this after Atraxas learns her language
Non Stacking Aspects
+5 Education
Stacking Aspects (5)
Education gives 20% more value
Megaprojects that require the allocation of Production are cheaper to build by 5% in material costs
Stacking Aspects (10)
gain +0.2 to the system bonus for Extraction and Production
Gothic: Unlocked
Non Stacking Aspects
Suspicion reduced for all actions by 1 per base 10 suspicion it costs caps at 10 reduction
Gives actions related to invoking Emps or the Tyrant within the Shogi system a +55
Salamanders: can be gained via the Salamanders
Non Stacking Aspects
reduces DAoT research DCs by 100
Stacking Aspects (5)
enables Atraxas to make Relics at a DC of 95 baseline, every stack reduces this DC by 5
Blood Angels: can be gained from successor chapters that follow the culture of the original chapter
Non Stacking Aspects
Suspicion reduced for all actions by 1 per base 10 suspicion it costs caps at 5 reduction
Stacking Aspects (5)
Increases the effects of other Styles by 20%
Exatari: Unlocked
Non Stacking Aspects
Research of Particle/Physics/Sensors/Energy are reduced by 200
Deep Infrastructure provides 20% more output baseline
Stacking Aspects (5)
All materials that are classed as exotics gain +0.1 production rate
Manticore Knights: Can be gained via diplomacy with the Manticore Knight chapter of Erimyst
Non Stacking Aspects
+1 Health
Psykers act at one skill higher, caps at Astartes Adept
Training is more effective
Stacking Aspects (5)
Effects of Health are increased by 5%
Order of the Golden Spirit: Can be gained via diplomacy with the Golden Spirit order of Erimyst
Non Stacking Aspects
Titans act as if they are a tier above their nominal level (caps at Low Primarch)
Training is more effective
Stacking Aspects (5)
Psykers gain 1 Tier to Faith