Rigging and animation

Ok I took a look in your code and model, there may be issues with the model itself. The first thing you can do is apply the rest pose, if you toggle between pose and edit mode, you can see there is a mismatch in bone allignment. To do that, simply go to pose mode, select all bones, then in up left menu, pose and apply rest pose. Next adjust the bone armature locations to the finger tips in edit mode, also adjust the bone roll to more or less match the parent bone. Also think about retopology and normals, 150MB is kinda overkill, this file doesnt even load for me online.