Hello and welcome to FF! I'm guessing your Pacman is 2 in. SVL (snout to vent) so a 5 gallon is fine. Pacman frogs can get stressed if the enclosure is big; but you can move it to 10G when it reaches 3.5 to 4 in. SVL. Around that time males start croaking and develop nuptial pads on their front legs "thumbs."

You can solve the humidity problem with aluminum foil. Cover the whole top screen with it and tape it to edges. Then use a sharpie marker to mark around your light fixture circumference. Using scissors carefully cut around the outline; but make the hole just a bit bigger (1 cm. is fine). If humidity gets too high; then just remove some more foil around the light fixture. Good luck !