The poly over Tru Oil caught my attention also. AFAIK, they are compatible, but I'm not sure what advantage there is to doing it.
I concur with jonwhitear about the sanding. Typically 240 minimum pre-paint, finer grades for wet sanding clear coat after it's sufficiently set.
FWIW, when wet sanding hand applied top coats like Tru Oil or Polyurethane, I find I can start with a fairly fine grade (eg:1000-1200) because they (typically) don't have very deep imperfections like orange peel that can occur from spraying. YMMV.
Edit:
I just had a look at the video XP referenced in post #16 and I'm not quite sure why the instructor is going to 1200 on unfinished timber.
That's not common practise IMO/E. There was a "debate" recently about "how fine is too fine" and my opinion (and practise) is minimum 240 if painting, 400 if I'm staining/dying. My 400 statement is what was debated by some, but I won't go there again now.
However for all intents and purposes, the general consensus is 240.