How many crickets he eats a day depends on numerous factors:
1) Size of crickets
2) Time of day offered
3) General activity of the cham
4) Cham disposition - some chams just eat more than others
I typically offer my cham food that is on the larger size. Whether you buy 1000 1/4" crickets or 1000 1/2" crickets, the cost is the same. But offering the larger crickets allows for more guttloading as larger crickets eat more along with the crickets lasting longer as he eats less of them at one sitting. Just make sure the crickets are not too large that he is struggling to get them down.
Also, don't feed him early in the morning. Give him several hours to get up to temperature so his metabolism is going strong. If the lights go on at 8am and you feed him at 8:30am, he may still eat but he won't eat as much if you had offered him the food later in the day. Just make sure you feed him and still allow for several hours under the lights to help him digest.
Also, some chams just eat more than others. Even brothers from the same clutch could eat different amounts. Just because my cham eats 12 3/4" crickets a day, doesn't mean that yours will do the same. Every cham is different. Experiment, try offering different variety. When my cham is sick of a food, he will still eat it, but he will not eat as much of it.
Another thing to remember, there is a lot of good advice on these forums. A lot of good general guidlines to follow. Buts that's all they are really...general guidlines or recommendations to follow. What works for my cham might not work for yours...there are just too many variations (housing, feeding, supplementation, climate, location, lighting, husbandry, just to name a few).
One thing I think most on these forums would agree too is that chams like a schedule or standardization (excluding food items offered). They like the lights on and off at the smae time every day. They like to be fed at the same time every day. They like to be misted at the same time every day, etc. Stick with a sytem and don't contastly change things. If you do make a change, make it a gradual one.