Reply to "Question - Can one black writable memory module hold both the cab and the base files simultaneously?"

1. yes

2. no, just write over the module for the cab update when you update.

One thing, even though you don't connect the second base to the layout, it's possible you cannot have it turned on in the same room as the layout. Only one base per layout, and I have had a completely separate test track pickup the signal from the base on the layout even though the test track was not connected to anything. So I would guess that there is a chance that a second base might interfere with the base you're using on the layout. Just a head's up in case you try having them both on and you run into issues.