We've got decades of stuff in that room that we're going to need to ruthlessly triage* and mostly chuck out. I'll probably take the chest freezer out and find a place for it in the garage as it's just for a seed bank, so not something I'll be using regularly. I'll possibly also bring up the existing shelving from the home gym/electrical substation so I can put a small sofa in there.
* apart from the books
I've also got some high impact parquet flooring of dubious aesthetic value that I'd earmarked for the open plan downstairs part of the main house that I could instead use here, and eventually get some better parquet for the living area.
There's also a small staircase in there leading to a door going up to the attic. I'm going to have to add another door at the bottom and cordon off that corner with dual plasterboard and rockwool insulation too. Otherwise the heat pump I'll be installing in there will just be heating the attic (the ceiling there is at an angle to get to the attic and is basically just plasterboard with daylight round the edges).
At some point I can also put my computer desk in there.
Sorry for typing out my vague to-do list on here...
@davep
Reminded of this film.
David Penfold 
Steve Williams