About #4, if the physical VLANs are correctly configured (meaning they exixts in the uplinks for the DVS and also for the std switches) you should not see any downtime - it is like a vmotion, the VM communication only changes physical switch port.
About troubleshooting... well, if you have the management network over DVS, and by any chance you loose the vCenter, or loose communication between VC and the ESXi, you will not be able to change anything on the DVS configuration, as it depends on the vCenter to work. Also, if by any chance you loose the vCenter (no possible recovery) it is very difficult to add the ESX servers to another vCenter and create a new DVS and erase all traces of the old one. You can't simply remove on ESXi usind DVS from one vCenter and add to another, it doesn't work.
I could be talking all night long about cons on troubleshooting... but everything, if well planned, can be recovered. Its only a matter of planning correctly the troubleshooting steps.