Pothos and some other larger leaved philos will do well with your pacman. If you having trouble with huidity I would dicth the ceramic heater and use an UTH heater. that will help increase humidity and warm the substrate a bit and even the viv if it pretty much sealed. I would aslo consider other insects like roaches and even pinkies now and then as a diet source. As far as impaction gos it does happen and short of a solid substrate like a clay base with a small pool your not really going to be able to completey prevent it unless you feed it in an empty misted tub.
Good luck with your vet check on the frog,

Michael