Open 0xr.space in the Quest browser or the free Model Explorer app, press Open and choose the .stl, then press View in your space. Binary and ASCII STL both open. The part is stood upright, since STL stands on Z, and opens fitted to about 70 cm; press Scale, then 1:1 Size, to see it at the size it will print.
STL has no unit, so a file 10 or more units across is read as millimetres and a smaller one as metres. It has no materials either: the model is light grey, unless the file carries the per-facet colours SolidWorks and a few others write. The whole file is one part, so the exploded view has nothing to pull apart. The scale stops at 10 cm and 10 m on the longest side, so a print under 10 cm cannot be shown at 1:1.
The size was guessed from the numbers in the file. A part under 10 units across is read as metres, so a tiny print in millimetres comes out huge. Scale it by hand with - and +.
STL stores triangles only. The grey says the file has no materials, not that something failed.
No. The longest side is held to at least 10 cm, so a smaller part stops there.
Yes. Download STL on the model's card writes millimetres, Z up, no colour. It needs a free account, signed in by an emailed code.
No. It is read on the headset, and nothing is sent to a server unless you create a share link yourself.