Some asshat wrote some tips
HERE that you might want to check out.
Could help you avoid some problems. Some other good reading in that section of the IBA forum.
If you both have the same strength of convictions, ride together. But, agree up front that if one of you starts slowing the other down, the other guy leaves him, and no hard feelings. If one of you smokes, do it alone. If both of you smoke, don't bother.
Nah, you can still do it, it will just take longer.
Preparing is like anything, work up to it. 500 miles is easy. Go ride 750 and see what bothers you. If you're covering 750-800 miles in under 12 hours, you're ready to do the SS1k. If it's taking you 16 hours to ride the 800 miles, you're not managing your stopped time as well as you could.
No, you can not witness each other. You need witnesses that are not on the ride with you. AND will answer the phone and questions if called. Read the documentation requirements. The point of all the documentation is to make it easier for the IBA verification teams to follow your ride on the maps and verify that you really did the miles. Do a good job on the documentation and it's a slam dunk for them. Leave a bunch of gaps and the phone starts ringing.
Tips can run all over the place. I don't know what you know and don't know, or how you currently ride. Get some LDComfort shorts or tights. Do NOT wear cotton underwear or you will regret it, especially in hot weather. Doing this ride in winter? Got heated gear?
You don't need to plan all interstate, but don't plan all secondary roads either. Keep to the big roads at night. If you do this in the summer, you can leave at 4 am and ride the whole thing in daylight after watching the sun come up on the road. Take the time to eat. You have 24 hours. I stopped for an hour lunch during my first SS and still took a relaxed 18 hours, even with the slow OR speed limits for the first 300 miles.
Remember that it doesn't matter if it takes 12 hours or 23:59, it's still the same certificate. Remember that your safe return home is more important than a piece of paper.
If you get the nods, STOP and grab a nap. Be prepared to just flop down in all your gear on a picnic table or the ground and catch 20-60 minutes of sleep, then go back at it. A bike cover makes a good, quick, body cover/ground tarp/sleeping bag. Nothing beats sleep if you're tired. Do not push on. People ride past rest areas all the time when they are zoning out from fatigue. They never see them. Don't be that guy.
If you micro-sleep, grab the next exit if there is one right away, or pull off the road and get away from the pavement, then lie down and sleep for what your body needs. If you're really that tired, you
will sleep. Once you become uncomfortable enough to wake up, you're ready to go farther down the road, even if that's just to a real rest area to get some more sleep.
Last tip - DON'T **** UP.