Help me understand CKOs

1. Is there a point in opening different chapter of an order in castles if I already have one?
2. Also, why can I get noble recruits and what are they good for.
3.I like the order of the silvermist but how can I recruit them?

1. Every chapter will occasionally spawn free knights and sergeants in the garrison, its good to have chapters everywhere, if you want to change chapter thats fine, but keep in mind that you might not be able to recruit some order troops without certain base units.
2. Noble recruits are your noble tier troops, the ones who can become knights, keep in mind that they will be from the faction your kingdom is, if you want to have pendor nobles, you must create your own kingdom.
3. You need silvermist ranger chapter in your fief and pendor black archers to train rangers.

You da real MVP. Free unit generator? Fug yeah!
But is upgrading the chapter in a castle really necesary? Do upgrades of the same order carry over in other castles? Also, how do I choose what equipment my order can use?

Upgrades in any chapter buff that order globally, if you have same chapter in castle X and Y, upgrades in castle X will upgrade knights and sergeants in the other castles, parties on map and even in enemy parties, so keep that in mind if you want to buff knights of the lion or dragon but have to face brennus or alexis later, its double edged sword.
You can give equipment to your own custom knighthood order-CKO through your steward. There are stat requirements and some items are unlocked when you do certain things. You need a bit more renown and honor as well as qualis gem to start such chapter and in the beginning they will be close to militia equipment wise, but later can become stronger than noldors. Training and gearing them takes A LOT of time, so dont expect miracles early.

If you haven't already, reading this tutorial might prove very helpful when creating your own CKO.

https://forums.taleworlds.com/index.php/topic,267392.0.html

About training your CKO, you can assign one of your companion to do this, preferably one with very good stats and, if possible, training skill (Leth or Sir Jocelyn for exemple). The main factor for improving your CKO stats is the difference between your CKO stats and those of the trainer (wether primary stats, skills or WP).
Therefore you should wait before uppgrading your CKO, wait until you gain very little from training, then upgrade.

spend 10+ gems upgrading leth and suddenly you can build twilight kniggets in your castle
you also need to do all the noldor equipment secrets too (1 at elacrai and 1 from capping noldor lord)