How do ‘assimilation effects’ work, in Endless Legend?

There's very little specific data about this in the game; for instance,

… does that 5% bonus apply to every unit you ever build? Or just Geldirus units they gift you / you build? What about the ‘per village’ part; is that per Geldirus village anywhere in the world (i.e. if I pacify Geldirus in several regions, can I get that bonus up to like 30%? Or is it forever locked to the 5/10% you can get from the one or two villages in the region you assimilate?)

Similar questions about city-bonuses from other minor factions.

(Also, how does this apply to Cultists? Do we get these bonuses from Converting, or only from Assimilating?)

(P.S.: I ask, because if it doesn't apply to multiple units, I'm not sure I see the point in assimilating any minor faction that you don't want the unit from.)

The bonus is multiplied by the number of pacified villages within your empire. This can easily be seen by pacifying 1 of 2 villages in a region you control and assimilating them. If you check the appropriate bonus immediately before and after pacifying the second you'll see it go up. This can make it worthwhile to assimilate a minor faction that is present in multiple regions to get a 3+ multiplier on your benefit.

The bonus applies to every unit you own, it is not applied when the unit is built. Unless of course it's a City or Army bonus.

I don't know the specifics of Cultist Assimilation