i think the best way to paint is to hang it over to put on the table / chair or on the floor. while hanging, the chance to spray evenly is better than others.

lol.. u not using any masking tape to the paper reiben? just stick 'em to the paper.. even a storming strike also your paper won't come out or fly..

sandal is the way too light bro.. if it's heavy enough still when the strong wind coming the air will go inside the paper and you can see the paper is moving just like in bloated wave

sometimes, the wind cannot be expect bro.. as a precaution i think it's better to be alert.

of course indoor is the best place, but mostly at home it's limited by space and irritation may occur.. or the chance to get scold by the loves one is high.