The first isn't really possible in the way that you want it implemented. You can make your armory add soldiers with armor to your city defenses, but you can't really "upgrade" the existing troops. All of the militias have set designs, and you'd have to design your own or switch the current militia to something that use armor (in which case ALL militias would get it, not just those from your armory).

The second, if I understand you correctly is really simple. Mana is just another resource, the spell cost part of spell can take any resource, custom or not. You basically make a spell that consumes 2 or 3 resource (including mana) to cast, and create whatever you want.

I have successfully done your first feat. If you don't mind I'll set up the base code and make it a seperate vanilla mod and you can modify and use the code for you mod.

It's up

https://forums.elementalgame.com/437988

Took longer because I was trying to make the tech tree look nicer, but it's there now. I don't know how to attach the armor to a particular building, but at least it's research dependent.

I made single piece suits to make the tech tree look nicer having one picture there instead of five or so. I hope that this was what you were looking to do.

Nicely done.  I gave some feedback on the mod thread but thanks again on this.