Okay...well I still havnt had a problem with any crickets, pin heads etc.
Yes gutloading is really good, I don't know about putting the calcium powder in the crickets food but what I do with my roaches is feed the dog/cat food pellets, and then I put carrots, lettuce, and any other vegetables or fruit like banana, pears, apple, etc but there are some foods you cannot feed them.
Veileds can get MBD extremely easily so you must make sure you have the supplementing down and right.
Its good that he is drinking chams can go fairly long without food but if they are not eating properley you will notice it immediately by the way they look.
And then about the crickets that are dieing are you sure they aren't dieing from the cold? I left crickets in the cold and they were stiff the next day with half of them dead but the other half just stiff and when they warmed up they were fine again.