Some research is required. Various streaming sites operate at different LUFS reference levels. I would find out what the ref level is for the site you want to stream from e.g. YouTube. This ref level is important. If mixes are higher than the ref level the streaming site turns them down.

You may have a premastered or even mastered version as of now. I would go back to the mastering stage rather than just turning down a mastered track to the required ref LUFS level. Get a LUFS meter and some are free and do a fine job.

Ease off your mastering a little and don't push the limiter into ref levels too far away from the desired LUFS ref level. You find you can get a more dynamic master a little easier in order to get a great sounding result.

If the mastered soundtrack is correct then the video editing software should import it at the right level. Or if it allows insert an LUFS plugin into the audio signal path inside the video editor. Final tuning of LUFS levels can be done there too.

If the track is at a fairly consistent volume all the way through then rms levels are usually around 2 dB higher than LUFS levels. e.g. for a -16 LUFS iTunes streaming site a consistent rms level of -14 dB rms about right.

You can save it in .wav format in Studio One and import it into Vegas. The exact settings would depend on what you recorded it at, 24bit 96k might be good but you might have recorded everything at 48k, either is ok. Vegas will accept a wav file that is 24bit 96k or 48k, however, depending on your version of Vegas there might be problems reading the file or none at all. If you do get problems then save it as .aiff and try that. This is the workaround.

I assume in the creation of your music video that there might be imported synced footage and some montages etc, just chuck all that stuff into vegas and edit away. You won't be recompressing anything in your wav or aiff file on the timeline. Then just choose the relevant compression format and levels for the destination when you export from Vegas.

If it's going to youtube, i believe the best format to upload is 1080p H.264 video codec within a .mp4 container, and the AAC-LC audio codec with a sample rate of 48 kHz or 96 kHz. Just blast off a few renders and see for yourself which might look best. Youtube should have some info about the best upload format to use. I hear you can upload 4k now so if you have the horsepower in your computer, film it at that leve, best to check with them. Go easy on the compression of your material since it will be compressed when uploaded to youtube.