A cage of this size could conceivably work fine for this animal, given some caveats. Usually the biggest potential problem with a large cage for a small chameleon is feeding, namely that the animal often has a difficult time finding the food becasue it is so dispersed. Cup feeding, as you plan to do, could remeady that potential problem.
I wouldn't be particularly concerned about the animal's ability to thermoregulate, if there is appropriate temperature gradient (basking area 90-100 F, ambient far away from basking area of 70-80 F). As pointed out, they do this in nature over distances at least this large quite effectively. Appropriate gradient in UV intensity is also important. These are basic requirements for any chameleon though, regardless of age or size.
Falling for an animal of this size carries practically no risk. It's often times hard to conceptualize how different falling bodies behave by virtue of different sizes. Small animals with high surface area to mass ratios create a lot of drag in the air as compared to large animals. As a result, their terminal velocity (the highest velocity they can attain while falliing) is much lower than for large animals. To quote a famous essay by Haldane,
"To the mouse and any smaller animal it [gravity] presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes."
While crawling around on some plants on our lanai (under my supervision) some time ago my female Jackson's (about 9.5" total length, maybe 5" svl) decided to jump, for whatever reason. In fact, she jumped off of the lanai itself, falling 20 ft to the concrete driveway below. I jumped up immediately, my heart in my throat, and ran downstairs expecting to find the worst. There she was on the concrete, a little dazed looking, but very much alive. She sustained no injury whatsoever, as best I can tell, not even a bruise. Granted, this is something that I NEVER want to repeat, but nonetheless, small animals, especially those smaller than about a mouse, land softly when they fall, no matter how far they fall. My chameleon is larger than this quite-safe range, so we were both a bit lucky. Something the size of an adult male panther chameleon would end up injured by a similar fall because it hits the ground much harder.
As for the cricket size, 1/4" is likely fine whereas 1/2" might be pushing it a bit, especially if the chameleon is on the smaller size.
cj
