Will humidity hurt my furniture and paint/fixtures while on vacation? Note: I left a few windows cracked before I left for a week
Normal humidity should do no harm to anything that's been properly made. Remember, humanity has lived with poorly sealed houses in humid climates for centuries, and our belongings have adapted to deal with that.

Woodworkers, for example, are very aware that wood expands and contracts as it gains and losses moisture, at different rates along and across the grain. That would cause trouble if everything was firmly held in place, so some connections are actually designed to slide a bit.

Other things make other adaptations, but o in general as long as materials aren't going to be soaked they will do OK.