Alright, if I where you, the first thing I would do is make sure my references were aligned correctly. You can do this by opening up the references in your favorite photo editor, and use some guide lines to make sure everything lines up. You want to use the major features of the reference as points to make your guides. Sometimes (especially when using illustration) things don’t line up quite as nicely, so you may have to scale some things to line things up. Most things line up pretty nicely here, so we don’t need to do too much scaling. Take note that the mouth on the front view is somewhat more open than the side, this could cause you a headache when modeling if you don’t remember things like that.

After everything is lined up, I like to have a pretty decent plan of what I’m going to be doing. Nothing perfect, but it helps to have an idea. This is especially helpful when you have a complicated reference, and you want to make some decent topology. Here’s what I did (nothing perfect, but it gives me an idea.) You of course don’t HAVE to stick to the topology you drew up, but like I said, I find it helps.

After that I dive right into the model. I’m prefer box modeling myself, so you had the right idea starting with a simple form. But my suggestion:

Start even simpler.
What you have going on right now is good, but I think it can be even better.
See the spot I marked? that would cause you some issues down the road, because of the lack of loops. Now, you could cut some loops in there, but that often makes a mess, especially if you don’t know what you are doing. I find it better just to have an area for the loops, and delete the faces and extrude (similar to how Pablo models in this video http://www.youtube.com/watch?v=M73HbKpYPv8 ). When you extrude, you end up with loops…so if you wield the extrude command well, you can easily make a decent mesh.

After using style of box modeling in Pablo’s video, I ended up with something like this:

(I’m not particularly proud of this mesh, I’m considering editing it out, it’s got a lot of problems. I don’t want to lead anyone astray. If anyone has issues with it, I’m not looking for crits, but I will take it down.)
This is by no means anywhere near perfect, I made it in a few minutes just to give an example of what you can end up with. If you want to see close to perfect, I recommend the following:
Keep going with your mesh, and post a WIP thread asking for topology crits. People way smarter than me will be able to tell you problems and solutions…but be sure to actually have something for them to critique if you ask.
If you like box modeling, I’d recommend watching this guy model.
His name is Martin Krol, he’s an excellent box modeler.
I’d also recommend checking out the “Poles and Loops” sticky, it’s got some great stuff. I know of people that come to these forums just to read that thread.