Thanks for pic Frank; it's a juvenile C. cranwelli and still young to tell sex. Well, let's discuss the tank/frog size relationship. Smaller Pacmans are kind of stressed by large enclosures, and a 20G is... huge. Also, Pacmans are wait and ambush predators, so the larger tank will make it harder to catch prey; unless you tong feed. To give you an idea; myself would keep a 2 in. either in an Exo Terra Breeding Box Plastic Terrarium medium (11.8" length x 7.7" width x 5.7" heigh) or similar critter keeper; a 5G tank; or an Exo Terra 12 in. cube terrarium. Even when full grown your frog will easily fit in a 10G tank; although would not move it there until it's 3-3.5 in from snout to vent (SVL).
Obviously your frog is eating, so maybe it forgot to get stressed

. But keep that in mind if things change. If it does, you have two options; get a smaller tank, or get a plastic keeper and place that inside the 20G.
The only things you need with frog are a water dish (prefer ramped ones) that fits whole frog with water to it's chin; shredded coco (mixed with dechlorinated water until slightly damp and begins to clump in fist without water squeezing out) to a depth same as frog's height; and a small plant to provide a sense of security). It will also help if you cover back and sides of enclosure to reduce stress.
For raising humidity would like you to please tell us how many watts is the heat lamp (and all other heat sources) and the temperature of room where frog is. Would recommend you cover with saran wrap the whole top minus area being covered by lamp(s). Do leave a 1 in. gap around lamp fixtures so the saran wrap is not melted by lamp's heat. Think that and couple daily sprayings should help with humidity. BTW, if using heat mat it should be on a side, not under enclosure.
Cricket should be same size as distance between frogs eyes. Can also feed night crawlers (not dyed kind at Walmart's sports section or bait shops) cut from pointy end around same length as frog. Food should be dusted with CA/D3 2X and vitamins 1X weekly on different days with skip day in between.
Hope this gets you started and good luck

!