That cage (as long as its made of screen) will be plenty big enough. These diseases are not inevitable. If you provide proper caging, lighting, heat, humidity, diet, vitimins/minerals, and a good stress free enviornment, (one chameleon per cage, not too much traffic, can't see other reptiles or pets) your veiled or Jackson's chameleon (i believe thats what you said you wanted) will probably not get a disease, however even with all of this care it is still posible. As far as the crickets go, chameleons have really long tounges, they might surprise you! I've never had much of a problem with making the container too deep so the crickets can't jump out. If there is, try making a little branch that goes into the food cup, but is still well above the crickets, the chameleon will be able to reach them for sure then. Hope this helps, don't get discouraged, the extra time and effort is worth it!