Why not use the little Kiwi dude then

- much cuter than sonic!.
I never got the hang of box modelling, I prefer to use segmented cylinders, like 4 x 6 sided cylinders in a stack to make the legs and feet, and something similar, but cut in half to make half the head. It can be a pain to make the head and keep the verts matching up - so if you work from a concept sketch, you can usually work on one half then mirror it. Works for me, and you can make good use of the polygon edges, which is important because you need to control where all the edges are to keep it low poly.
Keep UV mapping in mind too, because a sonic model won't be easy to UV map, I strongly suggest planning the model out on a UV map first, try and make it so you can plain map as much as possible, even if it means you copy the mesh and flatten it out then wrap it up again after UV mapping.
Van-B