For anatomy,I suggest you to study body parts separately from medical illustrations and from photo references first to understand the muscle topology, then study body postures as whole again from photo references or better from a model to understand the proportions of body parts and the muscle deformations. It will take time to progress you have to be patient.
For this project of yours, i see you are lost in subtle details like the textures of the forehand and missed your goal on the whole image. For example for a realistic human illustration, the feet are too big and too flat. According to shadows the joints look too deep as if they were squashed. The head seems too slow according to the shoulder width.
For the base anatomy illustration, I suggest you to use line drawing instead of shade painting so that you can figure out where the shades will be on the final image.
For the clothing,textures and colors I totally agree with tibbi.
For the T-pose, it is generally a good idea to draw the position of the arms as the forehands look towards the ground so that the animator’s job could be easier.
Overall, you need to observe carefully the nature of forms from real life and from accurate photographic references to understand the topology of things (human body, clothing, etc.)
and the interactions between them.