There is something interesting about your idea, I cannot deny.
Esspecially the idea with the Galadhirm Archers fits very well into the conception of Rohan.
One thing I definatley can put forward is the problem with the stronghold Helm's Deep the Edain Team will have in every case.
To speak from one's own experience I can tell you that this is a unpossible concept, although I like it, because there is no way to present it to the Edain Team successfully.
The stronghold of Helm's Deep is as unique as the white Tree of Gondor is or Minas Tirith is and both very denied to appear in the modification. Anyway, there are some upgrades which might be able to find their way in the mod. I would suggest to work with them, because the upgrades of the Rohan fortress as they are now are not very well done.
greetings
raschi