About which character you should work on, I would figure out the dog at the same time. The kid is leading the shot until the dog comes in, and you'll have to make it all work with the kid. Yes, you can mostly work on the kid first, just always double check with the dog. And the dog will be off screen until he comes in, right?
I like the way you end it now, it's a nice strong pose and build up to it too, great work!!
Silhouette wise, you're still in the same boat as before. On x138 the hand is in front of the kid's face and even on x146 it's still overlapping and forming a tangent between the hand line and the head line (on x193 the lines don't barely touch or overlap, so there are no tangents anymore). x205 has a muddy silhouette again.
In his pose around x225 after the dog runs through, I would open up his legs and not stay in the same pose. His right leg could be more stretched out. If you scrub through your scene now, the legs are always stuck in the same pose. It would be good for contrast to break them up after the dog attack, so you visually show through the pose using the whole body that there was a change and that the dog messed something up.
About the transition from blocking to spline, I would make sure that you have enough breakdowns before splining and in your case you will need more. Take for instance x83, 93 and x119. If you spline this you probably wont' have a nice arc going through that move and the timing will be pretty even. So by doing another pass with more breakdowns you want to solidify the timing of your actions. The spline conversion shouldn't really affect the anim too much.
Hope that makes sense!