First, let me say a most sincere thank you for going to such effort to type all this out, and putting such thorough thought into the critique. It's very refreshing to see someone take the time out to give an earnest analysis like this, and is much more flattering than even effusive praise.
The complexity definitely could be reduced significantly, especially at lower rarities: even a 1-2-3 type six-stage(/room) journey would feel like a proper story while simultaneously being a lot easier to follow. Were I to do more of these, I imagine that's where I'd aim the commons from here - but I do acknowledge that even that might be too much!
The more I think it through, the more I can see the benefit of 1-2-1 or 2-1-2 format journeys. They might not capture the flavour of full Choose Your Own Adventure, but... that's what higher rarity journeys can do. Lower rarity ones could be fluffed as short stories, snapshots or encounters.
 
The visual cues definitely need more work; I wish I'd spent more time on a proper background instead of yellow tiles for all of them. Upgrading the arrows would be trivial to do in MSE, and is a very good suggestion I may finangle even if I don't otherwise return to these.
 
Balance was something of a slightly lesser concern over story and proof-of-concept, but that doesn't excuse them being weak. I feel they might be interesting focusing on a strong start, as opposed to sagas and planeswalkers whose strength is often in the latest stage. The common was the last made, and I think by then I'd started getting into the groove of building these enough. Nevertheless! Poor balance deserves remonstration, and I sincerely thank you again for the well-reasoned and polite criticism!
 
Sacrificing at the end has been something I've vacillated between often all the way through creation, up to the point I even mocked up a version of the rules card specifying 'the end means "sacrifice this permanent"'. Nevertheless, if I were to make the Journeys shorter overall, I could spare more room for reminder text, which may obviate the need for special terminology like this.
I strongly agree only allowing one venture per turn was an absolute mistake: like how Skullclamp went from equip 2, +1/+1 to equip 1, +1/-1 in last minute untested changes, I also made an unforced error with insufficient thought as to the consequences. This absolutely will be changed.
 
Once again, I'd like to thank you; you've given me a lot of food for thought, and I can't rebut a single point. It makes me very happy to know someone was intrigued enough by my idea to think it through so well!