It should be interesting to see how long it takes Remus to figure things out; given that, unless something drastic has happened, both Andrew and Harry should have identical scents, I'd expect Remus to start wondering fairly quickly. I rather suspect it'll take Dumbledore somewhat longer. Even then, I'm not sure what either can do about it. Of course, given what Andrew knows, I wonder how much longer Scabbers will be free and what effect -that- knowledge will have on Dumbles; I suppose it's a question, then, of just how manipulating and scheming Albus is in your story.
As to pairings, I definitely like Andrew/Tonks but, if Harry's going to end up paired with a redhead, I'd much prefer it be Susan Bones.