Welcome to the forum. Have a read of the Archives of Wisdom here:
https://ironbutt.org/25tips.html
Read thru the info for the Saddle Sore 1000 ride and ask questions if you have them:
https://www.ironbutt.com/themerides/ssseries/index.html
Some of the important things to understand are that your dated electronic receipts are the official start and end times for your ride, not the signatures of witnesses. And that there is an electronic method that does not require witnesses to verify your odo. The Alternate method with paper witness forms is pretty strait forward too. You don't need a witness to verify your odo at the exact moment of your start. But you do need one within a reasonable time and distance. If you're starting at the gas station near your house at 2 am, you can have someone, (like a spouse or neighbor), witness your odo the night before. And the same goes for the morning after if you finish late at night.
If you're going to use the electronic method, practice with some receipts and your bike before the attempt so you can figure out a good method to hold the receipt and get a legible picture with your odo and the receipt. Don't forget that conditions will not be ideal at the gas station. Full sunlight or darkness can make taking the pictures more challenging.
The idea of your paper trail of dated business receipts is to make it as easy as possible for the IBA verification teams to see the route you took and that it wasn't possible to cut a corner. If you choose to do an out and back ride, clearly the turn around point needs to be documented, so pick a spot with an easy to get receipt for the time of day you expect to be there. Gas receipts are easy, usually, but it can be any electronic receipt with the required info on it. An ATM is a good secondary, just check your balance and get a receipt. Buy something if need be for a receipt. Even just a candy bar works if they give you an electronic receipt.
Depending on how far you've previously ridden in a day, consider going on progressively longer rides before jumping in and attempting a SS1K ride. This helps you learn if something starts to bother you with longer time in the saddle. A little thing on a 500 mile ride becomes a big thing on a 1000 mile ride.
It's very helpful to be able to drink water while riding. Many small sips is much better and keeping you hydrated than larger drinks at few stops. This can be as simple as a Camelbak style bladder, either worn or stuffed in a tank bag or just strapped to the seat behind you. Or you can make up a hydration jug for low cost with a 1/2 gal jug, a pot or pan from the thrift store that it fits into nicely, some tubing from Home Depot or the hardware store, (freezer line or food grade flexible 5/16 tubing works well), some bolts and removing the rubber cover off your passenger footpeg, then attach the pot or pan there. I've used plastic dog dishes even. A bungie cord or strap to hold the jug in place and a key retractor or card retractor leash to keep the drinking end where you can reach it and a bite valve and you're good. To avoid warm water in the tube, it's common practice to blow the water back into the jug after taking a drink. Others get all high speed and use insulated covers for the tube.
Eating. EAT real food, don't just spend the day eating power bars or something similar. You have plenty of time for a nice lunch. In rally mode I will hit an Arbys or McDs and get 4-5 small sandwiches to put in my tank bag. I like the Arbys roast beef plain, because there is no sauce to make a mess. McDs cheeseburgers taste the same fresh or 14 hours later. But rally mode means eating while riding, which takes some practice. For a SS1K there is plenty of time to grab something at gas stations when you're stopped already, just don't waste a lot of time lingering.
Nothing wrong with a few snacks on the road. Something sweet and something with protein is usually good. Keeps you from peaks and valleys.
Remember, it's much, much easier to save time by managing your stopped time than it is to make up time by going faster. No need to speed during a SS1K ride, just go the same speed you're comfortable at on any ride. The trick is to stay focused on the ride and not spend a lot of time stopped.
Doing the shorter rides will help you prepare for longer ones. Keep track of what bothers you and work on sorting those things out when you get home. Eventually the bike is comfortable to the point were you decide when you want to stop riding, not because something hurts or bothers you.
And if you're not enjoying the ride, stop. There is always another day.