kieleru, I don't think you've wasted anyone's time!
Re: troop training
There have been a few suggestions for a "hybrid" system (i.e., a combination of old and new training systems) that allows for units to improve slightly. If it is possible, I like it a lot. It allows you to develop those mid-tier, cost-efficient units slightly instead of having them be mostly expendable. Obviously, it allows you to get (even more) attached to your veteran units.
Currently, I don't think experience factors into the units at all. The effect of XP was disabled. I think that your suggestion of pooled experience providing party bonuses is an interesting one. My only concern is that it could lead to super parties in the player's hands when they already have an advantage because they are smarter than the AI. It is already possible to conquer swaths of Caldaria in a day, so I don't know if speeding that process up at all is better.
Re: fief improvement
You do you envision this system affecting the AI? Silverstag tries to keep systems the same for both players and AI lords. I like the idea of having to transform peasant recruits into militia to move them, but it might make the process too cumbersome. Still, I think it is interesting.
Re: companion party
Having sub-lord companion parties for smaller tasks would be really cool!
Re: companion messages
This would be helpful is some quest-based situations, in particular. You can send companions away when you get to the liege level; overall, I love the idea of bringing some of that later game utility to be early game. There are so many times where you just need to go pick something up or drop it off, and a companion—with the necessary relationship amount—could do it for you.
Re: automatic reading
If it is in their inventory already, it makes completely sense for them to move onto it when they're ready (if this is possible).
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Thanks for the read, kieleru!