Re: Power to 24v panel - easy to isolate?
The main feeder cable to the 24 volt panel is coming from the busbar-stud that sits on the wall that separates the battery compartment from the compartment that contains the main power switches. There are several cables stacked together there, one of those goes to the 24V panel. But be aware the 24 volt panel does not switch all consumers. The nav-area has a separate line. This also feeds the 24V-12V converters in the cabinet under the nav table. So disabling the 24V panel does not eliminate all power draw.
You may want to have a look at this product. It can handle 500A: https://tbs-electronics.com/product-category/dc-modular-fuseholders-busbars/
This means you can use it in your primary battery cable. Do think about how to connect this as you will need to be able to charge the battery even if the switch has disconnected the battery. So the charger should be connected directly to the battery. If I remember correctly Amel connected the chargers on the battery side of the main power switches as well. So even if you disconnect all power the batteries can still be charged.