As far as I've read, there have been no published truly scientific studies concerning molting and supplements. Everything I've read on the subject is anecdotal. As for iodine, it's not needed at all. Total GH is important, but it varies from species to species, much like pH.
The temperature range you list, in Fahrenheit, is fine for most species. When temperatures are warmer, say 80F and up, the shrimp's metabolism increases. The increased metabolic rate effects changes to multiple aspects of life, for the shrimp. The shrimp eat more and grow faster, they mature more quickly, and they die sooner. In essence, their whole life cycle is sped up.
I was curious about this and have done some experimentation. However, due to an inability to control variables, I couldn't definitively prove or disprove my hypothesis. I speculated that; shrimp living in a warmer environment (84F) would produce more young, given the same number of breeding adults, when compared to a control group (78F), and a group living in cooler temps (70F). I used Macrobrachium dayanum (Red Claw), and Neocaridina denticulata sinensis (Red Cherry) shrimp. Each temperature group had six breeding couples, in individual tanks. The difficulty I had was ensuring that each shrimp was the same approximate age. I ran multiple cycles, trying to get young shrimp that had just reached sexual maturity, to begin the experiment with. However, I was never satisfied that I had accomplished this.
I did find that I could keep my nursery tanks at 84F, to get the young to grow quicker. I then could move them to a cooler 78F tank for the rest of their lives, with no discernible decrease of lifespan.