Derp, I confused you with Fortis for some reason.
Yeah, I guess you do have mana for fog (although you can't cast it of course).
You might also want to have one of your apprentices cast summon snow there next turn. It isn't as good as the snowstorm spell would be, but combined with fog it should allow a pretty good ambush.
Yeah, I am planning on having Rapid Growth+Your entangling roots for the assault, I would like to send some plant minions in, but they wouldn't get there in time.
The dwarves look the nastiest to me, I don't know how dangerous they really are (since I don't have access to the raw numbers), but it seems to me that they are probably the toughest of the bunch (especially due to fog and how dangerous a ambush can be for everything else), and killing them will be hard. Focusing on others might be a better plan for now.
The calvary seem easy, using the roots on them while they are on their horses will probably topple them over, and since the battle is taking place in a forest they will have real trouble charging.
For the artifacts: It seems to me that just picking up mystical artifacts and just trying to have footsoldiers use them and hope they don't blow up in their faces might not be the best idea. I don't think ebbor is mean enough to have any of them have a potentially negative effect if unprepared, so it should be fine, but just throwing that out there.
Looking it over: I would wait till next turn, because I think that this battle has a very iffy outcome, you stand a good chance of victory, but you also stand a good chance of defeat.
Next turn you will get: +4 troops (my basic minions), Renewed spells+Ambush (which killed 8 in the initial phase last time), and full mana for the apprentices.
They will be prepared, but unless they get significant reinforcements (at least 5 dwarves/calvary, or 10 footmen), waiting a turn will still be advantageous.
On the flip side it will mean that the battle takes a extra game turn, so its up to you what you want to do.