First PH for hydro is 5.2 to 5.8. Keep it ther and all will be happy.

Now your water source. 225 is kind of hard wish it was lower and then you add cal-mag back to it. See the problem is you don't know what's in your water. If it were well water it might be good with iron and minerals but if it is from a water treatment plant then we know it is full of chlorine and chloromine and floride. Oh, chloromine is solid chlorine that does not evaporate if left out. But for now we will hope it's OK

Now for your rez and nutes. Mixing the nutes you got it. Here is the thing. However big your rez is. When you top off your rez you don't need nutes just Ph'ed water. Makes it easy. The rule is if you have ten gallon rez and you top off with one gallon PH'ed water a day then ten days and you need to change the rez. You have replaced all the water. No need to keep upping the nutes, they will get too strong when the plants suck up alot of water.
Once you mix your nutes forget about ppm's. They will go up when water is low and go back down when you add more water.
You need to change because your plant take up only the nutes they want and leave the rest and then they piss in your water or give off waste.

Your water needs to stay as close to 68 degrees as posible. An inline chiller is the thing. Your room can then be around 80. Most of us don't have chillers and need to keep our rooms at 70 degrees all the time. Works great for us. Wish I had a chiller then I could add the CO2.

Looks like your going the the right direction. Most all your reasoning is good and you have thought this out well.