I'd also prefer the first option:

It makes the whole set a lot more versatile, i.e. users could remove prop parts from the cubicle and replace it with a door, or a window, or whatever else they fancy. Or they could combine two cubicles, etc.
Having separate props instead of a solid object also makes it more useful for people who are lost when it comes to using the material room, unless you include a ton of mat poses... *1)

You could use a "Grouping" for P10 (or a "null" prop for earlier versions) and smartparent all items to this base.

This should be loaded first. Then, make two options:

1. Make the props load separately, and automatically smartparenting to the base "on load".
   However, instead of having to load each single prop from a separate library icon, I'd bundle them in logical groups, e.g. "floor & ceiling", "walls", "desks", "lockers", "chairs", "equipment", "plants", etc.
   Like this it would be much easier to load what you want, and them delete from these fewer items what you don't, instead of having to wade through a list of hundreds of props loaded all in one go.
   (But it'll require manually editing the .pp2 files, before distribution, in order to replace "parent ..." with "smartparent ...", which Poser doesn't when saving multiple props to the library).

2. For those who want it, include an "all in one go" option nonetheless - you could even provide this "extra" as a scene file, with some lights readily set up, etc.

I know this is going to be some extra work, but compared to the time you needed modeling it, it's zilch.
After all, you'ld want to make this item as versatile and user-friendly as possible.

Just my Tuppence...

-Peter-

Footnote *1) with a little "tongue-in-cheek": It would also spare me the effort of taking the "solid prop" apart again with the grouping editor's "spawn props" feature, for my own use ;)