You probably want some sort of circulation going on (not a fan directly on plant material, of course), but if you are controlling rh% tightly, the plant no longer is transpiring,, so temps and rh are all that matter for drying/curing. (light is actually primary cause of loss of potency, so darkness is important too)
a duct fan pulling air out or pushing it in will make your dehum/hum work harder relative to whatever impact your ambient RH is going to have.. are you in a dry area or wet area? maybe it's naturally 55-60% and won't cause extra work too.
I'd thnk twice about using a bathroom as nearly all surfaces in a bathroom are coated in microscopic fecal matter. Everytime the toilet is flushed, urine and fecal matter is aerosolized and spreads around the bathroom. you may clean the toilet and countertop, but it's all over the place, lol, and back on those surfaces you cleaned as the toilet is flushed.