I'll try my best to explain your first question;
I do not know how to create new unit card for units
There are 2 types of files for unit cards in the game. Icons and Mask.
It is easy to create a icon, but remember: both icon and mask size should be 64x152 (.PNG files)
I assume you can create a basic icon for your unit but you have some trouble with creating masks. Well here:
1- Open your normal unit icon in any graphical editing software (I'll use PS CS6).
2- Now select wherever you want to be masked on that unit card (I'll use "Polygonal Lasso Tool" -Çokgen Kement Aracı- in Turkish)
As you can see, I want my unit card only mask faction colors (or custom unit colors) for cloak, pants and some parts of his shield.
3- Now "Right Click" selection and "Select Inverse" -Seçimin Tersini Seç- in Turkish and cut that part (we don't need it).
4- Now desature the remaining part and done.
5- Also you can increase brightness of these masked parts if you wish.
I hope this'll help you. Have a good day!