I am arriving after the rest of our group. Is there anywhere close to the gorge that has overnight parking for extra vehicles?

Any idea the name or location?

Yes there is a campground on the way to the gorge. They also have parking.

You could probably leave your car in Vantage

We usually park our extra cars at the gadd station at the quincy exit

If you all are in standard camping, you can just walk over to their camping spot. You won't be able to park near them if you don't enter at tee same time, but no one will stop you from taking your tent to their area.

Not that I know of. If you're in premier camping you need to be there with your group. You can buy a Terrace camping parking spot for $50. You might not be able to get wristband if you are not with premier or terrace camping ticket holders.