Great questions. I wish we were at a point past all those questions so that I could give you concrete answers.
The only thing I can add is that we are stealing a page from another company practicing Holacracy and intend to identify fractional FTEs to roles. The tension that we're trying to address is budgetary, aligning funding sources to activities, and ensuring that role of lesser value or importance don't have more attention than roles of greater value/need/importance. For example: role A is only budgeted for 0.10 FTE and role B is budgeted for 2.5 FTE. People would then have a role and FTE equivalence calculation. We're prototyping this in excel at the moment but still a bit a way from having a running system that I can smile about.
Hopefully this concept helps give you ideas.