hey veggrower,
booting PPC mac from USB is not that easy 
If this would work, I had done it already, instead of using a DVD.
I tried this on my ibook for about an hour or more and did not get it to boot from the USB stick - I think on the PM it will be the same.
I was thinking, there could be some âcare about Macâ, because I think it is still the most of PPC´s out there, besides of some overpriced âAmiga-ishâ Systems for 2-3k Dollars.
I do not think, buying some cheap PPC Mac stuff was a mistake - it was for nostalgic reasons and for fun.
I know a bit and have some other devices besides G5 PM and ibook: iPad, iPhone, Nexus7, Apple TV, Apple watch, a gaming PC rig with VR ready GTX 980ti, and so on⌠oh, forgot my two old iPod 1st gen P
The DVD-issue is not the Player, it´s very unlikely. Like I mentioned, 12.04. 15.10. worked form live, only 16.04 does not.
I installed OSX 10.4.11 from DVD, also worked.
I agree, Linux is a great Option and thank you for the hints !
I tested 15.10 on a 1.42Ghz MacMini (which I sold), it was way too slow and un-responsive.
So 14.04 would have been a better choice, I believe. maybe next time!
Cheers!