Let me start by saying congrats and good luck!! sounds like you have made great progress!!
AS for your questions:
1. If you are sensitive to food, bring your own.
2. Even with SAG support, some supported rides do not offer repair equipment and I would hate to find out on the day of the event you are SOL.
3. For my metric century, I brought a lightweight cable lock to keep people honest since I was alone and no one to watch my bike. Ended up having the rest stop people watch it. Also brought 2 tubes, tire levers, pump or CO2 inflator (plus enough cartridges to cover 2 tires and an Ooops or to help someone else out), multitool, taillight, 2 insulated water bottles with electrolyte mix, NUUN tablets (or your favorite electrolyte - like Scratch labs now) in case they offered something I cannot stomach and can add to water.
4. Proper gear for the conditions - For my metric, it was promising rain and did drizzle on and off and later rain for a spell. I packed a packable rain jacket.
5. I also carried $20, ID, cell phone and a credit card. Never know when you need a ride or if you get hurt. Also had cleat covers in case I had to walk.
I went so far as to drive the route a few days before to scope out how bad the roads were and determine if two tubes would be enough and if I needed more durable tires. In the end, I was cautious where needed and didn't have an incident but I did see other have problems. It is always good to have enough in case someone else is not so fortunate.
To me, it sounds like you are very well prepared. For my metric Century, they claimed 3100 ft of climbing and I had only done 1900 during a 86 mile ride. I was also concerned. It turned out that they overestimated. It seems they used MapMyRide for the amount or something else but when i compared my previous metric ride to this new one, it was only 400 ft more.
I took the more challenging metric nice and easy. No hero or zero climbs and kept my pace such that I could easily carry on a conversation. If I found I could not speak (even to myself) I would slow down. When I got to the last 20-25 miles, I got tired of holding up and opened up the floodgates since I was still feeling good. My goal was to finish, not to set a record. If this goal is the same for you, this might be a good path to take. Stay easy on the ride until you have a distance that, based on how you feel at that point, you can turn it up. I premise this with the fact that I knew the course before hand and knew what to expect.
I hope you will post a detailed story of your ride. Will be looking forward to hearing how it goes.
best of luck,
Frank