StephenH

One source of knowledge is your local rando club- I'm not sure what that's like in your area, but check into it if you're interested.

How I got started in this was volunteering at an endurance race, the Texas Time Trials. Check into what's available (24-hour races are listed on the UMCA website). If anything's within driving distance, consider riding one of the shorter options, work as a volunteer, or just go watch what goes on. Plus at these events, you have a bunch of very experienced people.

Regarding equipment, that is very regional. It seems that everyone in the rainy northwest uses fenders, nobody but me and one other guy do here in Dallas, and I'm sure most of these people, when they go to to PBP, just take whatever it is they're riding anyway. So if you survey PBP bikes, you don't necessarily get a survey of what's fitting for PBP (or for Tennessee), but more a survey of who came from where. It's a similar issue with the handlebar bags. Recumbents are very popular here locally among the rando crowd, but don't seem to be at PBP. Visit your local rando club, go on a ride, and you'll get an idea of what they like there (which may or may not be what you want to use.)

A couple of tips on riding: My perception is that a lot of the local club guys get into a mental trap of riding very fast as compared to their capabilities and just assume that's how they should ride all the time, which effectively rules out any long distances for them. On your 84 mile ride, if you finished that and felt like you could keep going with no problem, great, you're doing good. If you finished that and pretty much felt whooped, then consider backing off on your speed a bit the next time around and see if that helps. (And just FYI, it looks like your average speed works out to 17.5 for that ride, which is faster than all but one of the rando rides I have ever done.) Generally, the rando rides will have controls every 30 miles or so (or people will stop about that often anyway), and if you did your ride more or less non-stop, taking those breaks may make it easier.

Secondly, rando rides in general tend to be hillier, so if you're headed in that direction, seek out hilly tough rides, not easy fast rides, and you'll be more prepared for what lies ahead.