The last question first - the PDM60 is just a distribution module - it does add any supplemental current, it draws directly from the battery/generating system.
First question - it really depends on what you are adding!
A head unit with a built in amplifier driving external speakers - no problem!
The example
@jholen gave with the WideOpen kit with a JVC HU/amplifier is only 10A max so WELL within the stock battery/generating system.
Adding a 1000W external amplifier? Now that's a whole different story!
The generator is good for 37A at 2k rpm (41A at 6K)
The std bike load of the R3 is going to be in the order of about 15-18A which still leaves about 20A of overhead for accessories.