Anyway, now for one of the most important points which is fitness. There's a whole (trash) board about that so I won't write much on this.
Being too thin isn't much of a deal and easily rectifiable, being too fat will greatly detract from the experience or make it impossible.
Body weight exercises and running work well and cost nothing.
Some elements on this can be found here despite the cringe title:
https://youtu.be/JhR8dk4RH4I?si=OONdkC38qDZ_vJT3&t=437Good sense is both understanding the terrain and being fair with yourself and your own shortcomings realistically. Many accidents and deaths happen due to people thinking themselves as fitter or more apt than they in fact are.
In order to determine the itinerary the trip must be planned carefully. Technical difficulty, distance, type of terrain, positive and negative gain and presence of water sources are some important elements.
