Nice story, not completely original but still enjoyable.
Notice you didn't specify the bonded/slaves had to be female. Not suggesting slash but that some male enforcers and/or spies might be useful and there is no limit on the slaves.
For the harem I would say a teacher(runes or arithmancy or astronomy maybe), the access a teacher could give would be valuable. Restricted section and the fact that Harry himself knows little of Runes or Arithmancy.
For Hermione I would suggest a slave, she would make a good research assistant. Harry could also use her or Lavender as distraction from Ron being around too much.
Another possible slave would be Madame Rosmerta, good info source for since she owns a pub and is usually described as quite the looker.
There is also Rita Skeeter to consider as a possible slave, the ability to control the press could be valuable and her animagus form makes her a good spy.
The last suggestion I would make is a healer, not necassarily Poppy. Harry gets injured way to often to not make that a valuable resource.
More soon please.