For your first question, i actually had the same one a few weeks ago.
here's the link to that thread : https://forums.tomshardware.com/threads/two-6-2-pin-connectors-on-one-cable-for-the-rtx-3080.3644762/#post-21965980
I bought a Zotac 3090 trinity and I'm using 2 separate cables just to be on...