you've already said that Dumbles isn't going to be happy. How far are you going to take that? Will he accept the changes in Harry and try to help him, or is he going to be all "This is for the Greater Good. Do as I say." or better yet, will he be pre-emperor Palpatine evil?(I remember one fic where the author had Dumbles put Bellatrix under imperious just to make her kill Sirius to get him out of the way)
As for Harry's power-level: if you plan to make him truely equal to Voldy try a block on his magical core. that would explain why he has occasional moments of truly impressive magic but is generally mediocre.
Author's response
Hey Bigshot. I guess the short answer is I haven't fully decided on Dumbles yet. My take on him is how I've painted him in my other fic - that he's not so much 'evil' as he is convinced of his own righteousness and that the needs of the greater good outweigh Harry's happiness. Also, that he doesn't truly know the extent of what Harry has been through; eg, he knows broad strokes but not details (since he didn't bother following up).
I'm not sure how I feel about the magical block idea. I've seen it used a lot of times, and I'm all in favour of a really powerful Harry, but honestly, I think his problem is more one of focus and discipline. I'll use the Patronus he cast to save Sirius and Hermione as a canon example of what he can do when he has confidence and focus in his casting.