Would it be helpful for me to share what I've done so far?

always! my pull request isn't functional, it's a mess of half-wired up scaffolds.

When I apply multiple tags to a bookmark I've only been able to get access to the last tag so far (this is what I'm looking into right now)

that's by design for about messages. you need to publish each about message with an array of tags.

I've been working on the model with a specific bookmark message and then about messages posted about the bookmark. I'm not sure if this will end up being the best approach but it seemed like a more straightforward place for me to start.

sweet. i think you should continue with whatever you feel best about, especially with regards to how you want to learn.

for me personally, after the conversations in %QRrL2wc..., i'm doubling down on my approach of publishing tags in about messages that link to the posts, since it can be applied as flags which i think is a very important moderation feature.