It seems to me like you have done all you could to reduce the polygons already. One trick is to open the model in magos, then open the model editor window, zoom out, and see where the red dots are the densest. On your model, it appears to be the hands and head. It is a bit unorthodox in wc3 modding to model the fingers, but yours are so well crafted and suits so well with the model that i think you should keep them. Second thing is, that before you export the model, make sure you select all the vertices and use the weld tool (with a tolerance of 0.1) on them, to make sure every vertex is attached where it is supposed to be. This can lower filesize (although seldom polycount).
When it comes to the head, i have just one advice to you, if there are any good references for what you are trying to model, USE THEM. By that i mean, setup two planes on your scene and texture them whith your reference of front and back. Align them to eachother, and then just do your model on top of it, trying to follow the outline of the background. Actually, you don't even need to add the reference to planes, just use views>background image, set it to "Match Bitmap" and "Lock zoom/pan", and voila! You have your reference in the background (this is for 3ds max). What i can tell from the reference is that the top-section of your helmet is inclined too much backwards, the visor is too flat, and the helmet is generally too tall. From a wc3 camera perspective it should look fine though.
Finally, some advice on animation. You have done a great job on the walk animation - few people can pull these off and make them not look hilarious.
Concerting the "spell throw", i have three tips:
*Try to always make every piece of the body move at all times.
*Always use your own body as reference - is it common for you to kick one leg back when you throw something? No, usually, it is the front leg that takes a step forward, and the back leg stays in exactly the same spot. Also, when you pull your throwing arm behind you while getting ready for a throw, you usually keep the other one raised in front of you, for balance.
*Exaggerate your animations as much as you can. The more motion, the more real they will look.
Overall, very nice model! I love the detail of the texture. The chest and shoulderpads are also awesome. I hope you complete it!