Typically if you want to DIY something you first start with the smallest prototype possible and work your way up from there.

This demo cell isn't super interesting on its own but to validate the chemistry it's super helpful. Once you got that done you'd then work on a stack of cells, say 10 or 20 or 40 to get up to normal system voltages.

Once you have that working it's just a matter of making the tank as big as you want for your storage. Provided the initial chemistry is reasonable you could probably use a pair of IBC totes and really go somewhere.