I think the easiest way to explain mastodon vs kbin is to compare mastodon to lemmy. (At least, this is how I look at it)
- Mastodon looks at the world through time-based history of what people post. The topic, or how many likes/upvotes does not matter so much as the time. Though replies to other posts are grouped together. This is how twitter behaves.
- Lemmy looks at the world through posts made about a topic. The time posted does not matter as much as the topic. Replies are called grouped under the posts by people in a tree structure. While how many upvotes usually factors into how the replies are ordered, there are multiple options on how things are ordered. This is how reddit behaves.
Kbin can look at the world in two ways, with "Threads" being a topic based one and "Microblogs" being time based. As they (mastodon, kbin and lemmy) speak the same 'language' you can load and interact with content across the software, just it will present it in the way the particular software thinks about the world.
I don't think so, but there may be a way.
Mastodon has the idea of 'Groups' (which are Kbin Magazines and Lemmy Communities), but it seems to not have methods of creating one. While you can subscribe to hashtags in Mastodon, I don't think they are equivalent.
Groups/Communities seem to be a non-native concept for Mastodon, but it seem to treat it as a person (from the short time I subscribed to a lemmy group/community from mastodon, it seems you get an update for every comment or reply made to any topic)
The idea of following a person (or subscribing to them) seems to be a non-native concept in Lemmy and there doesn't seem to be any way to support it.