Ideal reservoir temperature is ~68*f, it helps keep the most amount of DO in the nutes, without slowing their growth.
The PPM of your reservoir depends on what stage of the plants life it's at, the younger the lower the ppm then it raises with the plants life, then lowers towards then end then flush with plain water.
I usually run my cloner with plain ro water no nutes, then once they have roots and are transplanted I run them at 250ppm, then I continue to bump it up according to how the plant is consuming the nutes.
If your PPMs are dropping then your plant is drinking more nutes than you're providing and you need to up the PPM. If your PPMs are getting higher it means they're too high and you're plant is consuming more water.
Finding the sweet spot where your ppms don't change at all is where you want to be, it means you're really dialing it in.