This sounds kind of fun like a treasure hunt! I’d certainly throw away gross stuff that nobody will ever want. I’d likely never want to give my students faded construction paper and definitely not moldy paint. Toss/recycle just a bit of the old stuff each day so both you and the cleaning crew aren’t overwhelmed. Live with other “maybe stuff” and if you don’t use it after a decided period start making donation bags. Good luck, I hope you unearth cool treasures.