I put all my animations to a individual characters in 1 sprite. (logical really) Cos when I name that character, i can reference it by it during my program, and you can reference individual animations within that sprite.
Simply add all animations relating to 1 units in 1 sprite.
I would makke a sepperate layout (somthing like objects layout), and place the units on there.
And spawn/create them on the needed layouts.
Isometric is a tough cookie when it comes to decent imagery supporting 8 directional movement with animations, file size wise that is.
I have lots of animations, 8 directions, 8 frames per animation.
So each animation, for any single one character is at least 64 images.
In my current project: boad game, I have 7 characters, each character has 5 animations (idle, walk, attack, being hit, and death)
The images used are relatively small as I cropped the white space. (approx 120x150)
All in all, these 7 characters, 5 animations each, 8 angles, 8 frame per animation, already take up roughly ~50mb