It has been detailed many times what is in a stateroom.
Yes, but apparently Barracks contains the same. The barracks requires only 1 DTon per person for basic level of comfort while the stateroom requires 2 Dton. Both have a sleeping area, fresher, a food prep area, life support (heat, light, air and water).
The stateroom contains unspecified volume allocated to access but so must the Barracks. For a stateroom, maybe this is 1 DTon based on the wording in the section on floor plans, but depending on your interpretation these could be adjacent to the stateroom or scattered anywhere in the ship. Presumably it is only where crew require access to non-specific components as access within a specified component is included in the tonnage of that compartment.
Does the stateroom provide a small work area (desk, terminal and some storage space). Presumably storage is limited to the amount of luggage a middle passenger can bring (since the high passenger gets an extra Dton taken out of cargo). Is there space to study for example. How about accessing ships systems in an emergency or must you go to the bridge or an engineering station.
What are the beneficial effects of additional privacy. What stops a crewman from being able to operate in the same environment as a Marine and why.
FF&S (and similarly GURPS) gave the impression of rigour, but still make assumptions to simplify design that completely undermine them. Life support for example is per cubic metre of enclosed hull rather than per occupant. A single crew ship would need the same amount of life support as a 10 crew ship for the same enclosed hull. The other issue is that with too much granularity you start to see the cracks and if you have any interest in the area covered by the rules you start to see boundary conditions that should not exist due to unintended consequences.
As an aside, I note that FF&S considered 1DTon to be perfectly acceptable for military crews (2 per small stateroom) and even had rules for bunks and hot bunking.
The biggest turn off for me with FF&S (other than it was tied into TNE) was the formatting. You had to skip around the book and the on page indexing was frustrating. It was also too generalised to do justice to any specific equipment type. Revised to MGT2, with better layout and indexing it might be worth pursuing but you would need to revisit every single item of equipment in the game and I think that ship has sailed.