Powermac IEC C19 cable is present on Amazon and you can also easily build it yourself with the right connector.
About pice gfx card you have to use the default apple nvidia 6600 card for early startup menu and add a pc Radeon x1900gt/xt to boot into morphos.
At moment built in lan can’t be used, but you can add a pcie Realtek card (vert cheap) or a pcie Wi-Fi card Who can be based on various chipsets.
There’s already a thread about it.

I hope g5 quad will be soon officially supported by next mos release, even for fans.
At this time my powermac suffer of overheating with mos, while OS X and Linux are ok.