A little carpet adhesive, a few staples, a handful of small brackets, and it's almost complete! Overall, it's solid as a rock and has enough mass to keep it stable without anchoring it to any walls.
Only things left are a ramp from ground level to the second story across the front and potentially a hammock somewhere(I'm struggling to see where i could put one without compromising some other useful part of the tree).
Thoughts are welcome!
I think if I did put in a run, it would have to be as unobtrusive as possible, so floating shelves are more or less mandatory.
But I'm probably not gonna end up actually doing it, so the point is moot