Sounds like a plan..
Suggestion(s)
If it was my system,, I would pipe the two 300G tanks in parallel rather than series. My thinking is that would allow maintenance on one while the other maintains flow,, and during low water seasons, there would be less "bottom of the tank spoilage"
Additionally,, What is your flow rate? 600G is a big reserve. Given a family of four,, maybe almost a weeks worth? Might want to keep one inline and the other offline?
And use excess flow to run a gen-set??
My $00.0000002