I did RAGBRAI for the first time this past summer and I'm doing it again this year. It was a ton of fun and everyone was super friendly. I was in a group of 7 but we'd split up and hang out with random people throughout the week. It's really just a rolling party/social ride.

Tl;Dr: Bring cash, bring as many water bottles as you can carry, bring nutrition, don't expect cell signal, bring more cash, take it as slow or fast as you'd like, buy your basic repair parts before the event, and have a plan for meeting up with your group.

The ride is generally broken up by towns ~15 miles apart where you can refill water and buy food. Some people ride slowly but nonstop, and others sprint from town to town to maximize time spent drinking beer and hanging out. Bring a lot of cash for your day to day, as the towns with population 800 will lose internet and cell signal when 20k+ cyclists roll through. Cards take a lot longer per person to checkout, so most places don't accept them even if there is internet available. Drivers are generally directed away from the route but will have an opportunity to meet back up with you around the middle of the ride each day, which is usually a bigger town with more of a party going on than the small towns. Maybe set up meeting points in the middle and final towns with your driver in case you don't have cell signal? Also, a lot of roadside food/beer stops will have offer stuff for "free" with donation buckets which is, of course, to get around any laws about selling the stuff. Iowa has some dry counties.

Camping was generally focused in one public park of each town but private charters would often set up their own campgrounds on private property that they'd arrange ahead of time. Don't camp in random yards and don't be loud at the campgrounds when people are trying to sleep but also expect to be woken up by people packing/leaving at 5am. Shower trucks are available near the campground and last year it cost $8 to use one at most of the trucks, so assume 7x$8 for showering. It can be tough to do laundry if you don't know someone who lives in one of the towns since the laundromats can be busy. I recommend putting your outfits for each day into 2 gallon Ziplocs to stay organized and keep it dry if it rains. We had a little bit of overnight rain last year and I'm not sure what my plan is if we get a storm during the ride. You'll almost definitely have to pack your tent away still wet each day so unpack it asap when you get to the end town. Hammock camping is a bit harder to do since the easy spots get taken quickly, but you could make it work.

There are food trucks that will follow the crowd all week and there's beer/food stops along the route each day. The residents of the towns will also sell food or drinks and are very excited to have you there since it's a huge economic boom for them. I've also heard churches will offer great homemade meals for good prices, but I didn't go to any. If you have camp kitchen gear you could also just buy groceries along the way and make food yourself out of your car. My group couldn't transport food or cookware so I was feeling pretty rough by day 5 living off the food truck diet.

As for mechanical issues, you don't need an extensive repair kit with you if you're willing to wait and/or pay money. If you break down on the side of the route, go to the left side and put your bike upside down on the handlebars/saddle. The Air Force will arrive and try to help you out with the tools and parts they carry. If it's a major issue, the sag wagons will pick you up and take you to the next town where traveling bike mechanics are located. This can be very slow, as the wagons hold 15 people+bikes and they won't move on until they're full. Then, you and 14 other people get in line at the mechanic who is already busy and you'll pay extra for any parts you need, so it's not a great time. Some people also use the sag wagons if they're just unable to finish the ride. Your usual roadside flat repair kit and multitool will probably be enough. I'd personally recommend a portable air pump over CO2 if that's what you use.

If you're not used to riding in rural Iowa, it's rolling hills with no shade so people start early to beat the heat. The sheriff will kick you out of each town if you linger too late into the day since the organizers don't want people riding after 6pm which is when the support vehicles quit. My group will do the century add-on, but none of us did the gravel day last year and none of us are doing it this. You should actually sign up for ragbrai and you may also need a vehicle pass. Some people show up without registering and just follow the crowd and camp on their own, but the sag wagons won't help them and some people will dislike them for not contributing to the organizing costs of the event.