i vote for the patil twins to take the last two places.
and for the slaves, ginny, hermoine, lavender, the gryff chasers (katie, alicia, angelina), gabrielle, some milfs maybe narcissa and there are a huge number of girls he can use and throw.
and as mentioned it would be great if you spend time on why he chooses each girl. otherwise it becomes a PWP. even if it becomes a PWP, this is a good first chapter for me.