Interesting story, i like it. But you already have a flaw unless its intended. Tonk's last year at hogwarts was harry's 1st. Shes only 6 years older than him not 8.
Author's response
I think fan canon had it so they didn't overlap when I started writing this in 2010. I was going by the Harry Potter wiki at the time. J K Rowling has released a whole lot of extra material and bits of information since then.
Since it would have been very convenient for the story to have Tonks overlap with Harry, and I pretty much had this whole extra year before he starts in order to deal with that problem, I'm pretty sure I was sure of the dates at the time.
In any case it's not deliberately AU or anything.