As I said earlier, I am for removing that Imladris fortress, and with it, removing Glorfindel and Wind Riders. (I am aware of his role during second and third age, he helped in Battle of Fornost (From Lore that is his main link with Northen Kingdom, he leaded Elvish forces of Rivendell, Gray Heavens and Lothlórien against Angmar in the Battle of Fornost), so his implemention in "Help power" is enough from Lore aspects in my opinion. Also he should stay one of main heroes for Imladris, not for Arnor.
Agree, Lindon fortress should be at Outpost, and Rivendell's at settlement. My suggestion is to use current model of Lindon's Spire in both cases.
(http://media.moddb.com/images/mods/1/11/10679/lindonturm_1387493701.jpg)
For Rivendel could be used model of Spire lvl 1,2 or 3 (Think that lvl 2 is most fitting.) because it can be builded on settlement, and for Arnor Sprire lvl 4 of course.
I would also like to see Mithlond Sentries, (As you said Arnor needs some Tower Guards comparison, because this comparison miss, like there is comparison DolAmroth swordsman and Guardians of Arnor) and about that DolAmroth Knights comparison, I would like to see Mithlond riders with spears more then with swords. (Because of difference between them and Wind Riders and I found Spear/Pike weapon of Lindon's eleves. xD Because of vanila probably :D) Anyway, usage of current Lindon elven model into integration of this riders could pass, ;) and their usage into Mithlond Sentries's model is very fitting. These Lindon elven units of course:
(http://media.moddb.com/images/mods/1/11/10679/lindon.1.jpg)
In this case Círdan don't need that upgrade ability. And using of Palanír of Elostirion should be able only if Círdan is produced or somehow should stay requirement for Círdran's level 10. (This will complicate things, but it's justified from Lore aspects of that stone. From Lore is known that only Elendil could use that stone, it's needed great mental potential of person who wants to look into any of stones.) About mount, it is irrelevant in my opinion, because Círdan stays unit supporter.