I don't use Gatorade, preferring plain water. I do use Endurolytes though, about 1/hr for me. YMMV. Usually there are pretzels at rest stops which are good for salt.
2) Yes, avoid flaky people. I avoid long lines. I like to be about 4th wheel. Another good thing is find an experienced guy the size of a refrigerator and just sit his wheel. Because of his size, you might find that you're compatible and he won't expect you to pull. But it seems to me that a lot of people on these charity rides are pretty good. OTOH, I probably ride in the front 10% or 20% , so maybe I have a skewed perception.
If you want to get into a line, come up to between two riders who don't look they're together and point to the road between them with your right hand. Usually they'll gradually open a gap for you. I have a lot of experience with group riding, so I can easily see who's got it and who doesn't. But all in all, I haven't seen or had much trouble with riding with strangers. I avoid the obvious crazies. I avoid those who don't keep a steady pace. I avoid those who pedal a much different cadence than I do. I avoid hanging at the end of a long line. Bad statistics, and they accordion. I'll try a wheel and see if I like it. If I don't, I move up or drop off and look for something better. I like people who rotate off and let the next person pull. I never pull for more than 3 minutes. I never overlap, and I ride 6" to one side of the line of the wheel I'm following. A foot of gap for every 10 mph is good.
Of course it's possible to do it completely solo. Totally realistic. PITA though IMO. I like to get 'er done. Interaction is part of the fun of a charity ride for me. YMMV.