A Couple Questions About Upgrades (Armour and Weapons)

[Psyco]

I apologize beforehand for the size of the post

I'm planning on doing a small bit of modding (making castles more useful, etc), but before I start, I want to make sure I don't break anything.

Question 1- Can you make all units have "leather armor" and able to upgrade 3 times? If possible, how would I go about doing this (I assume start in the export_descr_unit, but from there, I'm not sure)?

I intend to make armouries something like this:

Building             | Cost | Effect
Leather Tanner         1000   10% Discount on Retraining (like the Hospitals)
Blacksmith             2000   10% Discount on Retraining, +1 Armour
Armourer               3000   20% Discount on Retraining, +1 Armour
Heavy Armourer         4000   20% Discount on Retraining, +2 Armour
Master Armourer        5000   40% Discount on Retraining, +2 Armour
Armour Factory         6000   40% Discount on Retraining, +3 Armour

I dislike the way that troops lower on the tech tree are so much easier to produce and upgrade than more elite troops, while not much worse. This change is one of a couple meant to combat this.
Is it possible to take a unit, Zweihanders, for instance, who could only get one armour upgrade (to bronze), and give them "leather armour" while keeping their armour value the same, so that they can get the full 3 upgrades? I assume I would also need to change something to do with the skins due to visible upgrades, but I don't know what (I have no intention of reskinning, so the further upgrades would use the highest upgraded skin available for that unit).

Question 2- Can you allow everyone to get 3 levels of weapon upgrades?
(I'm not sure that this question is valid, because although I assumed the Master Swordsmith would upgrade weapons by 2, this might not be the case)
Question 2a- Can you change the number of Garrison Slots provided by City Walls? Also, can you have other buildings give Garrison slots, and how do they interact (add together, only the highest counts, etc)?

I'm going to change barracks to approximately this (costs will probably remain the same):

HRE City (cities will have 2 Garrison Slots from Town level to City and 4 from Large City onwards)
Building              | Effect
Town Watch              Trains Town Militia, Spear Militia and Militia Crossbows
Town Guard              Trains Town Militia, Spear Militia and Militia Crossbows; +1 Experience to all units recruited in the Barracks
City Watch              Trains Town Militia, Spear Militia and Militia Crossbows; +1 Experience to all units recruited in the Barracks; +3 Garrison Slots (assuming that Garrison Slots add)
Militia Drill Square    Trains Town Militia, Spear Militia, Militia Crossbows, Halberd Militia and Pike Militia; +1 Experience to all units recruited in the Barracks; +3 Garrison Slots
Militia Barracks        Trains Town Militia, Spear Militia, Militia Crossbows, Halberd Militia and Pike Militia; +3 Experience to all units recruited in the Barracks; +3 Garrison Slots
Army Barracks           Trains Town Militia, Spear Militia, Militia Crossbows, Halberd Militia and Pike Militia; +4 Experience to all units recruited in the Barracks; +6 Garrison Slots 

HRE Castle (all foot troops are available from the Castle corresponding to the barracks that they would normally be trained from [Zweihanders trained from Citadel rather than Armoury].  
           All Cavalry require the stables [no cavalry trained from the Castle building])
Building          | Effect
Mustering Hall      +1 Experience to all Castle foot troops
Garrison Quarters   +2 Experience to all Castle foot troops
Drill Square        +2 Experience to all Castle foot troops, +1 Weapon
Barracks            +3 Experience to all Castle foot troops, +2 Weapon
Armoury             +4 Experience to all Castle foot troops, +3 Weapon

Would this be possible?

Thanks