The topology needed depend on the intend : if for gaming, it should be low poly for movie, it should be medium poly for image, it can be high poly
Note: it also depend on your computer performance.
In the image you posted the modelissation looks "clean" so you should not have issue later.
It is normal to have more poly in the face, as it conveys emotion. But it will still repend on the end usage.
Note: you make a high poly model, then create a bump texture of it and then apply it on the low poly model -> in that way your model looks like high poly but is low poly in reality.
Don´t model clothes separated form the body if you´re aiming for videogames. Try merging clothes and body as to 1 mesh. Otherwise duplicating weights it´s a pain. Good going. Smooth the arms with (edit mode-select vertices-press "W" smooth weights. Or when vertex are selected key in: "W-O".