My FAA CPL QXC was over 2 days and about 5-600nm. The DPE had no issue with it.
No it does not. Solo means exactly what it says - nobody else is permitted on the aircraft.
The FAA does not mention "solo". It mentions "performing the actions of PIC" or something like that. The reason it says this is because if one were doing the QXC in a twin, for the ME CPL, they know damn well no one in their right mind would rent a twin to a solo student or low houred ME pilot and so they make allowances for a safety pilot.
In FAA land it is perfectly possible to have a CPL ME and Private SE...I had this for a few days as I did my FAA ME CPL before the SE. Actually I already had the private twin rating but it is not necessary to hold this before doing the ME CPL. Doing the ME first had numerous advantages, not least that it meant I could do the SE CPL in a C172 rather than a complex aeroplane.