Measuring individual cell voltages in a series cells Battery
This approach might work... but it is far from optimal or safe. This is not how things normally done.

First, you need to minimize the drain on the battery form your monitoring solution. Optocouplers are not good for this.

Second, there are many more equally important things that need monitoring, like temperature, for example. Industrial battery monitoring solutions measure all that, estimate each cell impedance, life time etc. And they also monitor the integrity of the monitoring system itself.

Finally, there are proven solutions for this. Specifically - multicell stackable monitors, that can be daisy-chained for much simpler wiring than in your proposed solution.

Take a look at TI lineup, for example. The monitor chips like bq76PL455A-Q1 can monitor 16 cells and can be daisy-chained for up to 16 devices, for 256 cells total. Some of them even include balancing circuits (which you have no way of doing in your 162 cell battery).

So, my advice would be - stop trying to reinvent the wheel. Use proven industrial solutions with automotive grade components and your will save yourself a lot of grief.

Oh, and one more thing. I cannot imagine anyone assembling this kind of battery without thorough testing and matching cells first. After all, the battery is only as good as its weakest cell. So, make sure you get more cells than you need, label them (or write down serial numbers if they have them), keep a spreadsheet with all cell data. Buy a bunch of charger/discharger modules if you want this done under a month.