Fermax is minerals, amino acids, some yeast hulls and some Urea and Diammonium Phosphate. Use it sparingly in your beer, maybe 1/2- 1 tsps per 5 gallons. Since I don't know the proportion of how much nitrogen compounds is actually used, and how much "filler" at this point hard to say the toxicity to yeast in a starter.
Water, you can use warmer water but be WARNED, as mentioned above too high of a temp will kill yeast. We do follow Scott Lab recommendations, to a point, using water that is around 98 to 103 F. We also use a very sensitive and accurate digital thermometer to measure the water temp before adding the yeast. I have the same one here at home. They are not expensive and if you DO decide you want something warmer than 65 or so F water, then USE a digital accurate thermometer ALWAYS before adding any yeast to it.
We also use Go Ferm yeast hydration nutrient in our water before hydrating yeast. I found that very hot water (140 F) works great at getting that stuff dissolved, BUT and bit BUT we then add cold water to the 5 gallon buckets of water we use for the yeast hydration to get the temp back down under 104 F. We did 163,000 gallons appx. of wine in 2017 and over 270,000 gallons of cider in 2017 using yeast hydration water in the upper 90s to l03 F temps. I would suggest, as I said above, either get a decent thermometer, which you should already have if you're doing beer, and just hydrate at room temp water.