First off: Thank you for writing this. Nice to see people playing with the monrs. Secondly: I'm adding you to my favorites. Just so you know.
Okay, since you specifically asked about your take on the character, over all I liked it. The more childish aspects - the foot stamping especially - didn't quite ring true to me, but we all have our own perceptions of the characters. His lack of composition at the end also seemed a touch off, but I can't figure out why there...everything flows logically, given what you're doing and how you're presenting him, so it's hard to put a finger on it.
The bit about his pacing and his mother pacing? Bloody brilliant. I was also very fond of his view on politics and you did VERY well bringing the Muggle PM into at the end. His interaction with Percy was telling and did a good job of showing a "softer" side than the book did (softer, yes, but still controlled).
All in all it's a very well done piece and there's nothing I'd actively want you to change.