yes, you will need to clean cars out--both becasue you'll be sliding around, and also cuz you'll be carrying passengers in back seats. just get car cleaned out inside, you can leave floor mats and spare tires in no prob
there will be space in the school building to store luggage, skis, sub boxes, etc
yes, the skool is civilized, there is a fridge
no need for camp chairs or popup, there's a cabin at the skidpad with gas heater and picture windows to take in the action...tho it's well worth watching from close up to see what other students are doing right (or wrong) so dress for being outdoors.
key item--snug fitting shoes for fancy pedal work, forget wearing sorels or snomo boots etc