1) Personally haven't gotten through all the levels/difficulties, but I'd estimate maybe 20-25 hours if you're good at it/learn reasonably quickly? You can definitely get stuck though.

2) I think there's a bit of an issue in variety in that your scaling works about the same regardless of what strategy you go for (a ♥♥♥♥ ton of defense + whatever symbols you can grab along the way). But if you find messing around with different units to be the more interesting part, there's quite a few unlockables to go for.

3) No idea.

4) I think that autobatterls have not translated very well to roguelikes (I've tried most autobatterls+roguelikes like Hadean Tactics or Despot's Game and quit them pretty quickly). I think Vivid Knight is the best attempt at fusing those because the ability to retain synergies after selling a unit makes scaling a LOT more sensible (vs a lot of other autobattler roguelikes where it's just a rush to find the most degenerate stuff).

5) a) The aforementioned issue where the game is mostly about finding defenses before anything.

b) It's a bit non-intuitive to figure out how to get better. You can see a lot of posts with people struggling to clear Witch's House even 20+ hours in, and blaming RNG despite the fact that the game is not really all that RNG compared to a lot of roguelikes. It's just mostly because the way scaling works in this game is just non-intuitive.

c) Part of why autobattlers are great is because you get to see wacky ♥♥♥♥ happen without the pressure of commanding everyone. This game is not very good at that. It's actually sometimes confusing with what's going on, even.

Thank you very much for your reply.