You click "Dismiss Posts" if you want to remove the most recent notification but still get notified if something new happens in that thread on a later date. If you click "Dismiss Topics" you will never again get notifications from any of the topics currently in that queue unless you manually turn on tracking for them individually.
Uhm, there are no tags yet. They will be introduced in the next version of Discourse, but it might take a while until we start using them. Right now we're only using Categories & Sub-categories. There is a significant category-restructuring coming really soon though.
Actually Discourse automatically shows new users the Top tab, which displays the most popular (based on likes, views, participants etc.) threads on the forum. I've experienced this on other Discourse forums and I think it's a great way to get started on a forum.
That would indeed be cool, but unlikely to happen any time soon. Without even going into the technical challenges, agreeing on a common color scheme is ridiculously difficult and requires a dominant designer-mind to drive a singular vision through.
Thanks for the feedback! We'll look into that mobile editor text problem.
p.s. Your post would have been much easier to read in list-form. Check the editor buttons