I'm on a Sharkey instance too so I know the answer to a few of these:

1. An Antenna is a way to follow tags or keywords, you can create a single antenna with all the tags and keywords you care about and then check the Antenna feed/timeline just like you do the others. You can also create multiple antennas and each of them will be a separate feed/timeline that you can access from the antennas icon.
2. It's a custom web page that you can link to from your profile or posts, this was also a thing on tumblr.
3. It's basically a bookmark - there's also favorites which is basically the same functionality
4. You can add tags to posts, however do not add spaces to your tags - most of the other fediverse software doesn't like that. 2 ways to add hashtags: add the symbol to your post like a twitter post or add it at the end, or use the hashtag button at the button of the create post and then you don't include the hashtag symbol.

First time I hear about the instance and hadn't looked into the engine before, but it seems awfully like Misskey. And as I don't use Misskey much, I can't draw comparisons to what I see.

But at least from a quick glance for point 7, it does support tags: