@rightmeow I can take a stab at #1. This is just based on my experiences online with various communities etc, I have no inside track on info here.
TL;DR Forum threads are too chaotic and volatile to work with easily.
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Threads are an okay way to discuss something specific. They tend to fray into a lot of different directions, some focusing on minutia of some aspect, others on interpretations, relating other events, then arguing with each other, making quick comments or jokes, etc.
Then your original content creators intermittently reply where they can, both answering questions, and trying to stop or set aside certain tangents.
Timeliness, variable availability, etc all make for what you see here, really meandering conversations.
That's all fine when people are really just chatting, or brainstorming.
When you have something you are working on, or considering changing significantly, those threads aren't directly helpful. Imagine you are considering a character arc change in a series and fans are saying what they'd like the unchanged character to experience. It may be great ideas, but it's going to be scattered across pages and pages over a long time, and a lot of it may not be relevant if you DO make the change.
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DMs would hopefully be succinct, present an idea clearly, potentially use information that the sender didn't want public, and like posts also have a name attached so if needed you can ask for clarification, ask if a change meets their need specific etc. Like a +job thread on a game, if you're familiar with that format.
Ideally, after both internal (here being among admins) discussions, and those DM discussions, either a decision would be reached, posted and be done, or potential new content (here expectations, rules, whatever) would be posted for comment and either public discussion, or another round of DMs, or a mix.
TL;DR Forum threads are too chaotic and volatile to work with easily.