I have a 300+ volume tanks. I have a 25G ATO, but only filled it up to around 10 Gallons. I refill it every 3-5 days. Only filled up to 15-20 when I am away, for longer than 4-5 days.
It's always be safe than sorry. ATO could and will failed and you might ended up flooded the tank or run dry.
Also, everyone setup is different in evaporation. I recommended that you determine your evap rate and get an ATO container that better suite your need.
personally, like to check my tanks regularly. I recently discovered that my ato pump failed. Thanks to my, normal ato fill up routine.
BTW, nice stand build!