A fine read, Octopus. Well done.

Several things:

Fixed riders will experience much higher cadences on hills, and there is a need to experiment with this on the prelim 400 miles. In particular, a rider needs to ensure bike fit/saddle height is such as the hips don't rock at all when pedalling. If they do, even a little, the action is exacerbated at high cadence. There's also the body's unique "harmonic frequency" that the rider either should remain under or above -- I can't remember, but IIRC it's around 120rpm, and that's when it can be a bit disconcerting as everything jiggles out of control.

Practising the transition from sitting to standing and from standing to sitting also will become useful to help prevent struggling to maintain momentum (or stay upright!) in the first instance, and butt-slap in the second.

You might also mention a little about the need to consider crank length and BB height, or at least checking on the prelim 400 miles that the cranks aren't going to hit the road when cornering.

The rehydration point is vital, but there are some people who cannot take their water bottle from its cage while pedalling. Again, it's an acquired skill that needs practice, but to not learn it and wait until the rider stops could result in unintended dehydration issues.

I don't know if it's worth emphasising the need for at least a front brake. I think you are able to moderate downhill speeds with your legs; I can but I do so reluctantly to preserve my legs, and use my brakes instead. This also comes in handy to moderate cadence on steeper downhills.

Oh, and it might be worth pointing out that there is no shame in walking on hills that are too steep to pedal up. Some people get a bit uptight about the notion of "failure" if they have to get off and walk.

I can't think I anymore right now.