Well, I had some free time, so I made the schematics for the controller:

Slowly I am getting used to the KiCad. Made few components library, made a break-out board for the MCP23016, to test my idea of "selecting" the EEPROMs. I thought, I will simple connect all block-holders to the I2C bus directly, and with the port expanders, I will selectively power them. I hope, that the un-powered EEPROMs will not mess in the communication.

The 23016 is capable of powering the EEPROMs, it has a 25mA power capability per pin. Seems enough :) Next thing will be a breakout board for the EEPROM, at least two of them, to test it before I make the PCB. There is a voltage divider connected to the ADC of the ESP, for measuring the Li-Ion cell's voltage.

There is a level shifter from 3.3V to 5V, because I have read, that with 3.3V, the WS2812B is unstable.