Missions in CS

[Trin Tragula]

For example, the missions to build up your army and navy give you cheaper unit production....

Which means cheaper maintenance as well as cheaper units should you wish ti build more than the 75% of your forcelimit the mission asks for.

 

[Trin Tragula]

Those missions do compare your forcelimit to theirs first so what it means is that they can afford to be over theirs. It's still up to you if you wish to take the mission though.

 

[ForzaA]

You complete it, disband troops and re-recruit them. It only takes (assuming no other discounts to costs, further discount will make it pay off faster) what, 150 years or so to pay itself off?

What do you think you are gaining by disbanding troops and recruiting them anew?

Maintenance cost of a unit is equal to a percentage of the recruitment cost that *currently* applies to recruiting that unit. Disbanding a unit and building a new one with discounts doesn't make the maintenance any cheaper.

 

[Trin Tragula]

What about this one, "Prove legitimacy". Get your legitimacy up to a 100, then receive the reward of +1 yearly legitimacy

There's as far as I know no such mission/reward combo in the game.
The one I think your thinking of gives diprep as well as 0.5 legitimacy. It may have been changed between 1.13 and 1.12 though.

It's also a ruler modifier so it may last a while.