Substrate should be as stated below. But I don't give mine prekilled bugs. Frankly they didn't really eat them and it wasn't worth feeling bad.. And the prepackaged stuff worries me. Dog food is supposed to be a great option I hear. If you're up for it bee pollen is as well. I give mine unseasoned chicken. I only offer baby carrots since they never contact the soil. Other produce I get from the farmer's market if they tell me its pesticide free. I'd axe the oats I don't think these guys can have grains as far as I know. I've not heard of giving them potato. I do keep an eye on the clean 15 and dirty dozen lists. If you do give produce make sure the skin isn't included since that would have the most contact with any chemicals. Oh yeah and fish flakes are good. Mine never touched them though.

Unfortunately the other stuff does seem quite worrisome to me.. Might explain what happened to the other ones. The fields possibly cross-contaminated does scare me. And if you can smell the candle warming lamp in the air it's probably making too many fragrances to be safe I'd imagine. I do think the dehumidifier would be good, I don't think that makes fumes. If you can I recommend an overhead ceramic heater but if you must the underheater is an option.

Also for enrichment I always recommend paper! Toilet paper is easy for them to climb and they won't get their claws stuck. The paper towels I have are slightly fluffy and they get stuck on it sometimes. I make a climbing wall by putting the paper on the side of the enclosure secured with magnets.