Syncing Audio and Video
I do not fully understand if you intend to transmit live or not. Because you are using OBS which sounds like you want to go live, but at the same time you say you want to use Premiere to edit, which sounds like you want to edit and then publish.

If you want to record, edit and then publish, probably the best option is letting the Vixia camera record live audio and use it as a reference for Premiere to detect some of it and automatically sync with the new audio track.

If you are recording live, OBS has one feature to synk the delayed audio or video. Search "OBS Audio delay"



Regarding the question of the frequency... it depends on several factors. The main factor is output format+platform.

For example, Youtube recommends 44.1 kHz 24 bits for music videos. But accept 48 and 96 kHz.

There is some debate if 96kHz is even perceptible for humans or not.