II would have a float switch in the tank that controls a 12Vdc shutoff valve, and there will be a drain valve on the bottom of the tank for getting water. It is typically around 68 in the basement, so I'm wondering if I should add a heater.
Plan looks good except for one thing....the shut off valve controlling the solenoid.
When the large storage tank is empty, your 3.2G tank will not fill until the storage tank hits the float switch. That means no drinking water in the kitchen until it fills.
IMO, you want a mechanical float valve and a solenoid. You can control the solenoid with a mechanical timer or smart plug, so that you only make water for the large storage tank over night. That way you have water in the kitchen all day every day.
You can also get a 110 solenoid as well.......
Now as to heating, while it would be nice, I don't think absolutely necessary. Even if you changed 100% RO water, the tank would probably only drop to the low 70's. Not enough to bother most fish. That being said, I do heat mine, but I am changing 70%, and my storage tanks are right up against an outside wall of the basement, and are more like 65* in the winter.
It's a good idea to dose the storage tank ahead of time. Ca takes a long time to dissolve, and anything with CO3 to raise KH can send pH levels skyrocketing for a few hours or day until it comes into equilibrium. Also a good idea to have a air pump aerating and churning the water a few days before a water change. Stagnant water will not have much oxygen and the more you aerate it the easier it will be on your fish.
Hope that helps.