I did this ride last year and wore shorts, jersey, arm warmers, knee warmers, vest, headband, regular gloves, and wool socks and just removed layers as the day warmed up. The tough part temperature-wise is when you are waiting around for the ride to start, especially if you go down early to line up in the gold/silver start area. That can be a pretty cold wait so you may want to have some extra layers on for that. If you have someone you can hand-off the extra layers to right before you start, that's great. My friends and I didn't, so we picked up jackets/gloves from a thrift shop and then left them behind at the start. I've heard that the organizers donate unclaimed clothes to charity so the stuff we bought may have ended right back where we got it from.

For the times when you're not riding, bring layers. It's pretty warm during the day but it cools off as the sun goes down.

Have fun! This is a great ride. I'd love to do it again sometime!