This deck is meant to complement a deck with Boromir, Glorfindel and Dori. Dori will help Denethor defend before he gets a Gondorian Shield on him, or provide another defense if needed. Glorfindel will help Idraen ready with Asfaloth, and Boromir will suck in most of the attachments and resources from Denethor besides. This is definitely the support deck.
Here's the resources that don't go on Boromir -- Light of Valinor goes on Glorfindel, Warden of Arnor goes on Idraen, and Armored Destrier is useful to Denethor or Dori if Boromir doesn't have sentinel in planning.
One other attachment I don't always put on Boromir is actually Steward of Gondor. Yes, that's what you want to do if you want to set up the combo with it and Blood of Númenor/Gondorian Fire. And I usually do it if Boromir has a Song of Wisdom on him already. But I also like it on Denethor because he can still share the wealth with Boromir, and still trigger Heir of Mardil in the bargain.
Theodred gives his resource where it is needed most. He and Idraen almost always quest together, and Idraen will get it if she has no resources and A Test of Will or Hasty Stroke is in hand. If this deck is the second player, Glorfindel can be the target if he needs resources more than Idraen or Theodred.
The sideboard has extra copies of The Galadhrim's Greeting if threat raising or Boromir overuse make it necessary, Theodred can help Idraen build the resources needed quickly. Northern Tracker is for location-heavy quests, and Son of Arnor is for obnoxious staging enemies.