I don't how you would build units that graphically lose men one by one unless you use existing units that have that feature, and change them. I'd think that feature - for infantry and cavalry - is built into the unit class.
Graphic sizes
Infantry are about 3 to 4 inches per pixel
Soft skinned vehicles vary a lot, but average about 5 inches per pixel
Tanks are about 6 inches per pixel
You may learn a little about graphics/colours from this post:
http://forum.shrapnelgames.com/showthread.php?t=47320
Or use the search feature on this forum, and you will uncover quite a bit of help.
Cross