The thing is, square footage means nothing. You can't do anything without dimensions as you need to take into account wall thicknesses, door swings, and now you've thrown a staircase into the mix too. We need to know the storey height in order to know the geometry of the stairs. This will effect where the stairwell trimmers need to go to give sufficient headroom, how much usable space will be under the stairs, what effect the stairs have on the floors above/below them, etc...
What's the big deal with running the tape measure around the building? It will take minutes, then someone like me would be able to produce an accurate plan of what will fit quite easily. I don't know about anyone else, but you won't be getting a bill from me, so why not do the job properly safe in the knowledge that what you want to achieve can be done?