2 questions

I wouldn't go any warmer than that for springtails. You'll be able to tell when A culture is too dry or too wet. Dry crumbles and cracks and if it is too moist it will be liquidy and run. You want anything in between. It is most dependent on what kind of tops you use. I use coffee filters but have also successfully used paper towels. I would rather have mine more dry than wet because you can always add water later