I am not sure about the blue aluminum motor plate, I only have the standard m05. You might want look on the Tamiya website.

What do you mean by diff case? The diff is housed in the chassis halves, I would consider it fairly sealed. Its not sealed with an o-ring or anything, but dust and crap cant really make its way in there.

The steering is fairly tight and crisp, there is some vertical play in the carriers though. Not really an issue.

No, a servo does not come with the kit, only the RTR.

You will want a ball diff and stabilizer kit.