Why do you need intercession of anyone in the first place? Is God’s arm too short? Isn’t it His will that alone is done? Is someone going to change His mind. What if your “saints” are in Hell? then what? Isn’t God going to be insulted?
That's already been addressed: We don't "need" it.
Still I see threads on FR asking for prayers. I see Paul telling us to intercede for others, and asking others to intercede for him. Do you think Paul thought he "needed" the prayers of the Ephesians? Did he think God's arm was too short? Did he want something other than God's will to be done?
Isn’t God going to be insulted?
He was insulted at Calvary. He is insulted by every sin I commit. I put all my trust in His forgiveness, or, rather, I ask Him for the grace to do so more and more until one day He brings perfect trust from me.