EDIT: Just posted and already seeing messed-up grammar and spelling. Typical.
So, that went really fast. I missed all of it in less than a day. Anyway.
I think that those were overall decent choices. I love the ballista revamp. I would definitely suggest the invention of a thoroughly non-magical means of flaming and/or exploding projectiles for our ballista.
Yes, I realize this is long and goes beyond our present problem. But I want to roll all of these things into one, so that all our choices work together from the start.
Immediate issue DESIGN PHASE: Invent new ballista bolt(s), capable of lighting things on fire, preferably with a Greek fire-esque minor explosion/burn combination. Area of effect damage for ballistae? If non-magic, it would be better, since they might be inspired by our antimagic to do antimagic things themselves. Pottery-head bolts filled with oil and wrapped in burning, oil-soaked rags, perhaps?
REVISION ONE: Perhaps we can revise our arrows OR bows to be better at punching through platemail. Best option's probably arrows---revising bows for more power requires them to either be imbued with magic (AHHHHH EXPENSIVE!@!@#!) or made into longbows (Mounted archers are not improved, theoretical speed of fire is reduced, we don't know as much about longbows as they do, so the result may very well end up being inferior) with recurve and composite manufacture.
So, revise ARROWS for armor-piercing capability. We've mostly nullified their archers. make ours deadlier. If they've gone to the 15th century with their armor technology, we've got to go there with our bows and arrows. Unless anybody thinks we could invent firearms (Most likely not. Especially because the earliest man-portable guns----"hand cannons"---were woefully inaccurate)
EXPENSE CREDIT:
Bring down the expense of the palise shields. Get them out there among the troops. If we keep OUR numbers high throughout even the thickest arrow storms, we don't need to invest in magical protection. I mean, exploding magical arrows are cute, but when they don't explode and are stopped by a piece of wood, they're 99.99% useless, right? And that way, we don't need to invest in this ridiculously finicky magical business for simple things. Don't over do it. You don't need an impact wrench to remove a 1/16th inch bolt. I hope.
BONUS REVISION?
Is there no way to change the mind of an enemy? Could we, possibly, try a bonus revision on our read mind spell? It'd be risky, but if we could get it to allow the manipulation of the target mind, with the strength of the spell amplified by the minds of enemy/friendly soldiers touched by the zen-whatever component of the spell, we could conceivably sow a lot of confusion. While shooting the ever-loving crap out of the enemies.
As to acquiring the bonus revision, could we dedicate part of al-Mualiq's or whatever his name is (Sorry. Not.) personal guard to this guy's war? Best unit in the country, backed up by, perhaps, a squad of cavalry (However many will fit on, two, let's say, of our warships); mixed lancers/archers, plus the two boats they'll be sailing on. Put a single ballista on one boat, none on the other. Be expensive to lose, but hopefully not game-endingly so. Also, it sounds really powerful, especially what with our now more-powerful armor and ballistae.