Base-layer short sleeve jerseys or shirts. NOT cotton! Good biking shirts, with pockets. Then long-sleeve biking shirts, a fleece vest layer, and an outer wind-proof layer.
There are actually many different ways to do the cold-weather set up. This is mine. I’ve never needed more than that for this ride. On warm years, I didn’t bring the vest or the outer jacket. A biking rain coat is a nice idea. A garbage bag with holes cut out for the arms is the cheap alternative.
Invest in decent mountain bike shoes. Make sure the toe box is large and your toes have some wiggle room. Your front foot will swell by as much as 30% while pedaling. If your shoes are tight in the store, they will be excruciatingly painful after 20 miles. You want the shoe to be tight in the heel and loose in the forefoot. When tightening your shoes via velcro or whatever mechanism they're equipped with, follow this protocol. The strap closest to your toes is the loosest to allow for swelling. Middle strap is slightly tighter than the front strap. Top strap is the tightest, but not too tight to restrict blood flow or movement.
It is recommended to invest in a shoe with a ratchet or boa-style top strap so you can make on bike adjustments. Make sure your shoes have a decent insole with a metatarsal button for your front foot. Make sure your bike fit professional looks at your shoe and cleat alignment. Road bike shoes are not recommended and highly discouraged for this ride.
It is recommended to have short and long fingered gloves for the ride. On Days 2-4 where it is generally cooler, thin wool gloves are a great option as they keep your fingers warm but still breathe.
Riding induces friction in your nether region. One way to mitigate the effect is to use a cream which you apply liberally before you get on the bike in the morning and again at lunch. Your use of chamois cream will vary but it is recommended to have with you at all times (and a latex glove). Assos, DZ Nuts, and Chamois Butter are the highest recommended products and used in professional cycling. Don't wait until the ride to determine what's best for you.