Inception/Harry Potter idea query

So, today I started writing the fic where Arthur&Eames rescue and adopt Harry Potter.  I have a list of things that change/don't change from version to version, and I've made a list of Harry's yearmates in canon (according to the HP wiki).  The thing is, should I even out the number students?  None of the houses has the same amount, and there are three more boys than girls overall.  So should I toss in a few OCs, just because?

Also, the part I wrote today is McGonagall's, but who should be the narrator for Eddie's sorting?  I can't decide.