We use mutliple sequential insets on the TOC master page without any problems.
As long as you're happy with each being a complete paragraph, it seems to work well enough.
If you want paragragh fragments, you'll need tricks like run-in para fmts.
If you want the entire Flow A to be an inset, watch out for PgfLocked.
LOP is easy. Suppose you have a source document with this structure (example):
And you want the checklist doc to just show this:
The checkllist doc can be made by doing a LOP (Special menu) that pulls the "Step" para tag, and then change the "StepLOP" para tag in the LOP to autonumber with a Wingding box glyph, not the enumeration used in the "Step" para tag. Finess the rest of its formatting to make it look right and you're done: any update to the source procedure doc(s) will propegate into the LOP when you update its BOOK.
Another cool benefit: the StepLOP lines can be set to be hyperlinks to the source doc, so if someone doing the checklist doesn't know all the SubStepsx for it, just click to find out, then use Back (Alt+Left Arrow) to return to the checklist.
Yes... the group for whom I work is trying to do something VERY similar.