[ first of all, I know am such pain in the... but...I'd say, just as a different possibility, not saying is better or that, just in case you could try and make the pectorals a bit taller... And probably serratus muscle a bit bigger would benefit as stands in comparison with latissimus dorsi (dorsal) that is good that it appears that powerful for this character(making a good bone-weights rig of it is...well, you'll see 
But perfectly possible), but pectoral and serratus(exterior, specially) are probably too small (and there's one more group than in anatomy , in abdominals... the lower one must be way taller, indeed, "ombligo" should come upper, and that last division should dissappear ) ]
All that little comment is in case you'd like it to add, if not, is only I can't avoid it, happens with anatomy and proportions, can't stay with m y mouth shut.
Now to the question:
It depends a lot on:
a) your 3d tool of choice.
b) the way your brain deals with 3d
I mean, there are point, nurbs , box modelers, and many other ways... You can achive it with any technique, though at the end you gotta deal with polygons and editing polies at fine tune level...
That is, you could model with nurbs, and at some stage convert to polygons and tweak.
I'd attack this sort of model with subdivs (what you call box model: I moedl since long with Wings Mirai's methods, which are based on edgel loops and other powerful operations, so is not only box modeling ) , as tends to give a lot of control, and helps with doing th einternal non detailed structure first, of rough volumes and go to the detail progressively. With subdivs you can achieve a very hi res detail (I've done) while keeping the model light, and way more under control.
I'd advice to do so, and at a very specific moment (in my case, when Wings starts to die, usually at a bunch of thousands polies) , you could import into Blender (or Zbrush) and do the hi res thing. After all that is for generating a tga we call normal map. Also, in my experience at least, dubdivs allow me to...once I have some thousand above the poly count I have been asigned fo rthe model, I stop there, and re-wire it so to make it game engine friendly, re-wire the joints for nice bending of shoulders, etc, and if I can, some organization that wont make it crazy to uv map. Always with quads and ngons. I only triangulate temporarily before export, and I tweak it a bit before export.
This way, once at that point, you have your game ready mesh. Then you continue, imho a lot yet can be done in Wings (or Silo, Modo, Maya, etc) to keep with the mesh control and the machine cpu and ram happy.
Once it's not so, and the kind of detail is not so optimal to add with Wings, then I jump into whatever the high detail modeler. I have Zbrush, but Blender with an average machine , allows doing the job. BTW, Blender can it easily half a million polies in a carppy machine. Ask that to most comercial modelers with same machine...am not a crazy fan, that is a fact.
Also, this way is more friendly with Blender's latest method(non stable build in graphicall.org) for doing tangent normal maps, (so, good for animated characters) , as is better if the low pol model adjust well to the later high detailed version of the model. But don't get constrained to it: may be faster and optimal to just , go to the hi res version with no worrying, and later retopo over the hi res (there's paint retopo and other ways available) , that is, you paint the wires over the mesh, the first one to have the hype about this was topology brush of Silo. I prefer the other way tho...But that's me.(indeed, retopo has some advantage...depending on how late you exported to zbrush...i mean, if basic volume masses are the same, no issues, if not, you may have to tweak the low version a bit so to match well the hi res...not an issue, tho )
I mean, you can, in the way, do whatever, use splines, nurbs, etc, tracing over the omages...Nothing is written in stone. Just if later you convert to polies is less controlable than subdivs. IMO.
And to make this model with subdivs, I'd go, load to "image planes" in Wings (or whatever similar in the tool u use) put left view (btw, I liked it) , and another for frontal. Notice how important would be tho that they matched every element in height, I tend to use guides for this, drawing all model views in same sheet... Still, I only model so when paid and forced to do so: I prefer to make a free drawing, and then base on it in my mind, and add or remove stuff as I go modeling. But bosses want ususally the other way. However.
So, you'd block those image planes, add any primitive, or just a plane, and do a cut , 9, for example for the edges, and roughly adapt the shape, and then some more cuts, etc, this part is to get a rogh shape...you extrude the silouhette, and go to left view (Z key ususally) and now is more of standard modeling, cutting etc, to go getting the mesh fit on that left view as well. You'd probably need also a top view, but as I say, when doing a free project, imo would be an over kill: you can capture it all, and after all, your drawing seems is not a written in stone design, for games, you can usually enrich it as you go...
Then use all the power that wings, mirai, silo, modo, etc, have for modeling, you have there more than enough.
I don't uv map in Wings, but in unwrap3d. Where the uv mapping power is really crazy. But I often do a test rig, very fast , of shoulders and some other delicate point before taking the task of uv mapping. When you reach the anim part, you will notice you'd have liked that the shoulders would have all degrees of rotation with no strangling.
But...you can model however you feel... Only counts the result, and of course, the time saved, and making it enjoiable...I only enjoy with things being not over complex
Modelling, uv mapping, texturing, rigging, and animating a hi highend character of this days is hard enough by itself
With subdivs and other clever methods in other tasks, I keep enjoing it, tho is all quite a time consuming task , hehe.
