Depending on whether this is simply smut with no real plot or if it plotdrivenn smut the choices for the Harem could differ.
Your own proposals for the harem implies that it is smut without real focus on the plot (as others before me have already pointed out)
If you want a bigger focus on the plot, than Ginny is a must for the SSS since she has been identified as a powerfull witch.
Hermiones position (SSS or slave) depends on whether making her a slave removes her thirst for knowlegde, since that is truly an asset that shouldn't be lost, and her abilities with magic implies that she is at least somewhat powerfull (though some of it could easily be through hard work).
With Fleur In the SSS, I can't see what Gabby could give when it comes to power (if Veela powers even transfers through the bond), so at most she would fit in the slave bond.
Parvati never struk me as powerful, and being twins they shouldn't have a big differens in power, only in dedication, so I would prefer them as slaves.