Caelum vs. Arcoscephale

[Azhur]

I'm playing a PBEM match against my good ol' friend. Here's the current situation:

Map: Arduria
Province strength: 6
Magic Search: 55
Random Events: Rare
Victory condition: by victory points
AIs: Pythium, Man, Ulm, C'tis, Marignon, Pangaea, Tien Chi

Turn 17

Caelum (Me, SE of Arduria):

Provinces: 27
Forts: 2
Income: 1300+ (Top)
Gem income: Way above all

Fire +3
Air +9
Water +4
Earth +8
Astral +4
Death +1
Nature +11

Research: Average
Dominion: Top
Army Size: Top
Pretender: Flying rainbow mage

Arco (He, NW of Arduria):

Provinces: Less
Forts: 1
Income: Less
Gem Income: Much less
Research: Top
Dominion: High
Army Size: High
Pretender: Ghost King SC

Till now my friend has nearly always beaten me. Now the payback time has come and I want you guys to help me to win this battle.

I'm expanding to the west and recently killed Pangaea. Now I had my first encounter with Tien Chi and so far no problems.
My friend is struggling against C'tis troops, which seem to be dealing much of trouble for him.

My primary tactic for now has been Wind Guide with High Seraphs, and as you can see, it has been working splendidly for now. But my fear against Ulm and such has also made me buy some Mammoth/Wingless squads.

My greatest weakness is the usage of magic. The only real deal I know for Caelum are of course AEQs, but other than that is beyond my knowledge. I've researched Conjuration and Construction 3. I've got lots of gems (especially air and nature ones), but yet no use for them. I just found some sorceress (2N, 2?) in the north, but don't yet have good ideas for their usage.

So.. how should I proceed?