I THINK. those numbers you see effect the adjacent states difficulty. like Massachusetts, it's a 3 star difficlty state, but if you've liberated the states surrounding it, you get a bonus to you chance to complete the missions.
leveling your assassins, from what little attention i've payed to them, seems to give them better weapons, and tools....and a beter chance at surviving battles(cuz good lord do they suck at level 1....but rock at level 11)
I haven't noticed a change in any of the rewards for the final repeatable mission in a liberated state.
No, i don't think so, but i think there might be an ingame trophy. --- It took hundreds to kill me, but I killed humans by the THOUSANDS!!! Look at me!!! I am sublime!! I am the TRUE face of evil!!!
When you liberate a colony, it gives you a bonus to missions in the colonies adjacent to it.
Leveling up your assassins does make it easier to complete those missions, but it also makes them better in combat when you call them- they're more resilient, get better weapons and are able to do more moves.