on prisener mode you will get some slut level, but I gues if you keep watching for all desires and keeping them under 50 (just let it go up to 35 and than supress), you should be able to beat game under 50 slut level easily. Also you should farm levels on first floor. Yeah... and never get beaten, that's really bad for that.
For shop best thing is money - start with those parts which saves most of money - and when your order is low, just buy something for that (+ control), but just when you are under 20, lower order means more money. When there is no more upgrade for that, get some control, so that order is not decreasing so fast and than skills, you will need that to beat enemies at higher floors.
Also there is that thing with being exhausted, I'm not sure how exactly with that, but when over 50, go to bed. Maybe upgrade your bed.
And last tip, for boss, go to sleep and get to him without any atacks, you need to be 100% fresh there.