I don't think it's mathematically possible to pay all debts from all stages while staying «pure» (or doing no lewd scenes at all).
I seem to remember reading that there is one (and only one) such scene in the recollection room, but that you need to cheat your file for money to get it in a play-through. Since you can activate switches in the recollection room that let you see all scenes, you can just do that, instead.
What I find best is to both progress the lewd scenes as fast as possible, and pay your debt as fast as possible at every level. (But only when the lewdness requirement for next stage is met)
It is entirely possible to grind every dungeon until the very last day for every level, but then you accumulate so much money that the monologues that Grace has to justify doing lewd scenes ("I have to choice but to do this, if I want to have enough money") start feeling totally disconnected from reality