1. Rejuvenation is easiest to achieve from cities, but as you noticed, it is useless too close to the city. As a result, you are best off deciding which direction you want to rejuvenate, and snake that way.
Outposts can provide rejuvenation, but it is unclear whether it's a bug, or an (un)intended effect of some improvements. The effect is certainly unreliable.
There is a rejuvenation spell, but it is stupidly expensive, and does not always work. I play without restoring, so I never bothered to figure exactly what makes it work or not.
2. There is one quality of roads, but if there's a nearby outpost, you can upgrade it with a stable, and then you can go even faster on the road.
3. Henchmen and scions are special. In my guide, I have them as a separate unit type, 'sidekicks'. How exactly experience is awarded is the topic of one of the concept entries. Short version - they do NOT reduce the gained experience.