I've been meaning to do something like prestige classes for some time, but I'm still pondering how exactly I'll implement them. For now I've settled on just having classes as stat spreads, having skill selection be the main source of character customization.
As for repeatable missions, couldn't come up anything interesting concept wise. I might just settle with using each of the girls unique talents to unlock new ways to tackle quests(Melia locking doors, Lyra distracting guards, Natalih healing civilians).
While I want to further develop the RPG side of the game, I'm still committed to five H-scenes a month and I won't neglect the eroge at the expense of the RPG side.
tldr; Every RPGesque feature will be develop with leftover time basically.