• With Crusader Kings Paradox has got Feudal dynastic politics nailed from an insider's POV.
  
• But with Stellaris they've got a good structure for modelling galactic conquest, trade and independent factions

• By the time of the Dune trilogy, the galaxy has been largely explored, so the game can't have Stellaris's lengthy exploration phase, nor much claiming of unowned systems
  
• A large proportion of it already controlled by the Padishah Empire, and most of this is already governed through its vassals (much like Charlemagne's medieval Europe under his Holy Roman Empire).
  
• Most likely you will begin as an Imperial vassal and expand, not into free territory, but into those houses who do not have particular favour with the Emperor.

"You're just one small sandtrout in a very large galaxy"
~ some Fremen kid's mother somewhere on Arrakis

• You start as a minor vassal dynasty of the Padishah Empire (maybe like the early days for the fledgling Atriedes and Harkonnen houses, prior to even their becoming Dukes).
  
• The Emperor's strategy is to juggle his ambitious vassals one against the other - to ensure none get too large and threaten his control.

'From little things, big things grow'
- Paul Kelly (Australian songsmith)

• Like in CK3 this is a time for feuding with you neighbours and gradually expanding your territory. You start out with one or two Star Systems (equivalent to Counties in CK3) trying to conquer enough systems to claim your first Sector (equivalent to a Duchy).
  
• As a small house, the Emperor happily nurtures your dynasty as another tool in his arsenal.
  
  • He periodically grants gifts to those in good standing (much as the Pope does in CK3).
    
  • Later the Emperor offers you missions. If you succeed he grants rewards of planetary systems, commodities, military units and status perks etc.

"Pride goeth before destruction, and a haughty spirit before a fall".
— Proverbs 16:18

• By now you control enough related Sectors to claim a title equivalent to 'King' in CK3 (how's 'Star Lord' sound?) Your 'kingdom' could be a traditional Constellation, I guess (drawing a pretty outline over a patch of the Galactic map)
  
• But as your realm expands the Emperor begins to fear you. Instead of offering you missions, he orders you to undertake them. Often it's unclear if they're meant to assist your House or imperil it.
  
  • The player may wisely opt to delay dangerous missions. But rejecting them outright will invite punishment.
    
  • There will usually be a variety of ways to carry out most missions - military, diplomatic, intrigue, economic etc.often employing the aid of external factions (see below).
    
  • Your choice of solution may reduce your risks, but may also effect your rewards.
    
  • Of course the Emperor will eventually get quite pedantic over missions - perhaps insisting you employ only military solution, and lead by your treasured Primary Heir. Or another mission he nay simply make unreasonable demands about raising your Spice contribution to the Empire (so I hear).

"Oh what a tangled web we weave, when first we practice to deceive"
~ Walter Scott's Marmion

• Cautious of imperial retaliation, you build up your power with subtlety if possible - with a view to surviving the End Game crisis now looming on the horizon, but not provoking it prematurely.
  
• By this time your dealings with various factions and secret societies throughout the game will be maturing towards one or two solid alliances.

There's quite a range of Dune factions to collude with, just starting with these:

Bene Gesserit - Matriarchal coven of psionics, manipulating the dynastic houses in their centuries old project to breed their galactic messiah. They rely upon the psychotropic Spice Melange for their abilities.

Bene Tleilax - Amoral merchants of gene-engineered organisms (clone warriors, human computers, doppelgangers) . Many of their products have become essential since a Imperial ban on Artificial intelligences.

CHOAM - A galaxy-wide cartel of big business and financiers

Fremen - Tribal group with the potential to halt the flow of Spice, the galaxy's most valuable commodity. They share some prophetic insights with the Bene Gesserit, due to their constant expose to this drug.

Ixians - An fringe technological culture providing mechanical devices that test the Empire's anti-technology proscriptions.

The Landsraad - An assembly of all noble Houses in the Imperium, meant as a check against excesses of Imperial power wielded by the Emperor

Spacing Guild - Guild of spice-mutated 'navigators' with a monopoly on faster-than-light travel. Also a faction wholly dependent upon the Spice supply to operate.

"Cry ‘Havoc!’ And Let Slip The Dogs Of War"
~ Shakespeare's Julius Caesar

• Eventually a now thoroughly paranoid Emperor will declare all-out war upon your House. This triggers a galaxy wide 'Realm Divide' between all the houses and factions (similar to that mechanic used in Total War: Shogun 2 by Creative Assembly)
  
• You can preempt this by declaring war on the Empire yourself early - but this may effect just what allies you get (some find joining wars of conquest more, or less, attractive).
  
• But it's all do or die now. Your victory or defeat will be granted accordingly