Yes the 8MB code of CoW are written by me and Eagle by Hand.
Okay let's see:
16ms for one Unit or all?
I guess you underestimate the complexity of Advance Wars for the AI.

But i guess you'll find that out sooner than later.
CoW mainly uses three classes for the AI.
The PFS (Path finding system or Wegsuchsytem) this is the stupid think showing the fields you can move over in this turn for humans.
The CoW systems adds some extra logic here. You can force the PFS to find the nearest city enemy,etc. and return the path to it (including some extra information that i don't remember in detail)
The base AI class provides some useful functions for all AI's like calculating dmg and some more stuff.
The derived AI classes have some extra logic again.
The AI's up to the Medium AI don't consider fronts or how much units to send their since in 80% of all cases. You only need to find the nearest enemy.
Everything about it takes a really huge coding that is tested in the Heavy AI (but i can't say anything about it now) since it's a alpha version right now.
First firing with indirects and then by directs makes it easier for the AI to move.
The AI's use the prices of a unit or the movement range of a unit to prioritize which direct unit is moved first.
(not true for medium or heavy AI)
That basically covers the easy AI-Strategies.
For the medium AI e.g. the AI calcualtes how much units of the enemy can attack a field and how much dmg they take + how much units the AI has in this area....
It getting quite complex here...
For the building system the very easy AI just spams units that are cheap or if it has enough gold more expensive ones
The easy AI works similar to the AW2 AI which uses a kind of builing table (5 infis 1 tp 2 landers one transport copter) everyone knows this with some extra logic behind.
We have a more complex system checks which units to we have how much dmg do they deal do which enemy.
Is there an enemy we don't deal dmg too e.g. a Copter or Bomber.
Find units that deal dmg against this unit. Build it.
(This system is configurable with an ini file and can be forced to be used by all AI's) This means you can change the AI so it builds the Units you want to be on a map you created (only on this map)
or even more complex which units are around this base have we units to deal with them here? Build it...+ Try to build enough units.......
As said the 400kb only cover the basic logic.
So it's getting quite complex.
Have you calculated movement maps or areas of influence?
Yes and that's not easy at all.
For how to reuse or calc map influences. The AI creates a virtual map of the game calcs stuff here (before moving anything (this acutally takes 1min) since the AI creates a lot of information here) and use this information to do moves cheking counter damage etc.
And maybe you try the CoW AI's one time
viewtopic.php?f=37&t=12896&start=80 and check if the AI is strong enough in your opinion.
The problem is the code here is over 2 years old + i'm currently working on the network for CoW.
And after this i either rebuild the Battle Animation System since it's glitchy as hell or continue testing and rebuilding and throwing away code for the heavy AI. I have some ideas here but i need to test them in the first run.
The heavy AI is in English but as mentioned alpha code the AI doesn't crash but i have to change a lot of calculations here e.g. making them comparable and and and...
Take a look at that class if you want...
but in the end AI for AW games is complex complex complex complex and i'm just a stupid guy trying to program something a whole company couldn't do. You can easily beat an AW AI in any game so....