Clean and disinfect the space thoroughly.
Clean outside the space where things may get tracked in or bugs hiding that will be enticed by plants later. Clean Clean Clean.
Seal it up from bugs, light leaks, air leaks etc.
Make the walls reflective, add some reflective materials on the walls. There's a a few different things you can use depends on budget mostly, and if plants will be up on tables or something, consider that you dont really need to use reflective material from the table height down below the plants, although you could.
Just a few things off the top of my head.
That's a wicked sized space!