Hi,
it´s near holiday season so I keep my answer short for now:
1. Yes, I modified MPP so we can use Parts in Step. I mainly work with a 3rd layer for these Parts and role them up to the Operation Consumed Parts. End users can add their Parts to the Steps, but EBOM/MBOM validation is done on Operation level. From my POV, it´s the most "easiest" approach as you don´t have to rebuild the complete EBOM/MBOM validation. This one requires changes in some ItemTypes, Methods, Codetree, XML Schema Elements and one Form. Yes, it´s a hell of a customization.
2. I have done some rollup of the cycle and setup time, so think you should be able to roll-up everything. As far as I remember there is even some forum post about this one available.
3. I don´t use additional Document elements so far, but I think it´s possible to add an additional XML Schema Element for this one. I don´t think it´s hard to do, but you need to know how the MPP components sticks together (Methods, XML Schema, Codetree,..).
