I'm hoping to build a similar system in the next year or two. Biggest difference is I plan on building battery banks out of lithium-based 18650 cells. You can salvage them from old laptop batteries, even dead ones (one bad cell can bring the whole battery down, even if the other cells are fine). 18650s are also used in Tesla's car batteries [0] and Powerwall. They literally just cram thousands of them in there. There are some youtubers who have done tons of stuff with them [1][2].
[0] https://youtu.be/NpSrHZnCi-A