Hi learning01,
You are on the right track and you are doing good! Yes you are correct that the number of slots continues over to the second chassis as what essentially happens is we are creating a larger logical grouping of the interfaces and hardware on both units into a cluster. This allows you to have a single pane of glass if you would when configuring the system, so that you can easily manage everything as if it was a single entity.
So yes, in your case, if you are using the first slot on each chassis for your SFB, then you would configure the respective fab interfaces as you've suggested. Just make the config on the master, no need to do anything specific on the secondary device.