1. glad to hear you have a good sized enclosure
2. 2 white's at most (in my opinion) should be kept in this size enclosure, but I'm sure this is not what caused your frogs demise
3. You should invest in a hygrometer, about 2-3 bucks at the petstore. the humidity should always be at about 70%
4. that's a good temp for daytime, lower temps at night.. night temps 70-75
5. spring water is fine, as long as it is 100% spring water. Tap water can be used as long as a water conditioner/de-chlorinator is added- found at your pet store.
6. that's good, it's the fine coco fiber right? so there is no risk of impaction (severe constipation) from eating the substrate as white's can do when the dive bomb their food items
7. that's sounds fine. be sure to have plenty of climbing space and hiding areas
8. fine, but be sure the crickets are not larger than the distance between your frogs eyes. too large of food item can cause impaction
9. This is the biggest problem I see. You must dust the crickets! Calcium every other feeding and vitamins once/week. there are many different brands on the market, all work fine. both can be found at the petstore. a calcium deficiency can cause MBD (metabolic bone disease) causing seizures, lethargy, and death...
10. that's fine, be sure to have a consistant day/night cycle. 12 hours day, 12 hours darkness
11. your using a spray bottle? this is what most people use
12. frogs can go for many days without eating, but if it's not typical for him, then that could cause worry
13 - 20. this all looks fine....

I would guess that the problem is calcium deficiency. start dusting those crickets! even if your gut loading the crickets, it is so imperative to dust with vit and calcium.
The fall at the pet store could be a factor, I don't know, it's hard to say.
Good luck, and hopefully some others will chime in.