1: What is the simplest way to record on the PC via USB
As Sydney wrote: just connect USB, set proper routing in 01v, and find some recording software (Cubase - is bundled with the mixer, Reaper, Audacity,...)
2: Is it possible to output all the PC audio via USB to the o1v96i? (ie I'd like to be able to play video clips etc on the PC with audio going to the o1v96i via USB).
Use the same USB cable - you can send 16 channels of audio from PC to 01v. That means 8 stereo pairs that you can mix in the console, i.e. start several videos, and mix the sound in the PC, or you can cue one while another is running - although that requires some clever routing and some free channels in the desk.
Problem could be if you want to use two applications at once - one for recording and one for playback - that might be tricky. Try to use ASIO application for recording, and WDM (normal windows audio) for playback if you get stuck.