Even a cheap analog thermometer is better than nothing to get an estimate on temp. I would not worry about getting it too warm (unless 100+F) as long as you have the crates stacked up to create a temp gradient. I find my adult males like to stay higher up. Not sure if it is because it is cooler, or that is just the way it is. (I keep mine at around 85 degrees on the bottom of the tub)
This may sound like a stupid statement, at the same time make sure the "dead" roaches are not just their old exoskeleton from a shedding. Other than weight, they look about the same.
I am no expert which is why I can state the following:
They are easy to keep! I have had mine going for about 6 weeks and have a good number of little ones. I just followed everyones advice on this board, which all seems to be the same. I posted pics for you once, and upon reviewing others, my setup is correct.
I feed a variety of veggies, ground up cheap dog food and fruit (mostly oranges). I have a smaller container that I use to gutload the roaches on-deck for feeding. There I use the premix from blapticadubia.com and they seem to eat it fine. I also use water crystals because they are cheap. It is true that the roaches can get their moisture from fruit/veggies.
I am not sure if I saw all of your pictures, at the same time I noticed that you are using egg containers for their hiding spots. If you have not already I would suggest switching to flat crates, or at least offer a larger area of the egg containers. I do not think that the dubias like to be crammed all together. My group has distinctive areas in the container for adult males, females, and young. I did not create it this way, they established this on their own.
This is all I can add other than make sure the temp is correct. (And don't use as feeders until the colony is established!)
Jim