I would just add the Fitch to the current shavings and mix it in together, as she is settling in. I had them mixed for a while. Then next time you do a clean you can swap it for all Fitch. It'll help keep it smelling familiar to leave the shavings in and mix in with the Fitch.
Sand potty sounds fine. Good luck cable tying things to the bars
I find it a real fiddle. As long as it's stable I'm sure it'll be fine
They can still hurt themselves falling from a height onto a wood bendy bridge, so it would help to have something like the Sputnik hanging over it.