Hi Richard,
There seem to be some inconsistencies in your plans...
The prototype station is straight but your model space is L shaped.
The bit of the prototype you are interested in, the shed area, is relatively simple and well-defined but the peripheral bit that you are less interested in, the passing lines, are complicated and extensive.
To model the shed you only need storage space for locos but if you model the mainlines you seem to be thinking about mainline traffic, which will need much more storage.
I’m sure all these things can be resolved.
One idea might be to use just one leg of your L shaped space to model the shed area with simplified mainlines either in the foreground or background just as a non-working scenic element?