[Deeda]

Sorry you haven't had any replies yet.

One downfall I see is that your top off reservoir may run out of water if you don't fill it in a timely manner. Also not sure if display tank water has the potential to backflow to your reservoir during a power outage?

Have you considered just using a dedicated water line with a filter combo that would treat for chlorine or chloramine depending on your water supply and either an electric operated solenoid with a timer or irrigation setup with a controller?

 

[Deeda]

I would think raising the new water add tubing above the display tank water level would work well.

If you aren't in a hurry to get this project done, wait a while and maybe look through other topics or wait for someone with more experience.