Help with Custom model import

I am attempting to give my self a custom player model via creating a 3d model for some armor then using the animations of the current player model to control the new model like a puppet, while using a procedure to make the texture of the vanilla model invisible, but I have hit a snag, I was attempting to import the block bench file when it told me that there was a 3x3x3 limit on cubes and that the model I made went over that limit, I am unsure what this fully means. if anyone has a work around I would appreciate it very much if you shared it with me