Now this is what I call a classic. Great smut, hell, great story in general. You know it's a good story, if it would still be good without the smut. Wouldn't mind seeing Harry with all of the female Blacks in canon (Bellatrix, Narcissa, Tonks, Andromeda), but since you said no to Bella, Narcissa is done, and you've already mentioned Tonks as a possibility, I guess the only suggestion for them is Andy. I liked the way he tricked Cissy, and can't wait to see the reactions of other girls to Harry's prowess. Recommend Pansy for another Narcissa style payback.
Interested in Gabby being one, but isn't she like ten or something. I know they said she was eleven in Deathly Hallows, so a year prior would make her ten. Hope you have something planned for that.
Also, I'm scurious as to who Harry's teacher was.
For other girls, there's always
1.Su Li- who gets way too little play
2.Eloise Midgen- acne girl, but acne clears
3.Hestia Jones- older women
4.Parvati and Padma- TWINS!!!
5.Alicia Spinnet- don't see her much
6.Penelope Clearwater
7.Lisa Turpin
8.Tracey Davis
9.Millie Bulstrode- big girls need love too
10.Sally-Anne Perks
11.Madam Maxime- see number nine (just kidding, unless you think you can pull it off)
12.Random females, or OC (wouldn't recommend, but it's your story)