Not yet. Threads has announced fediverse Integration as "coming soon." When it does, you'll need to find an instance that federates with threads. Most of the fediverse seems to be losing their fucking minds over the thought of it right now, so you'll probably end up having to search for a while for a federated instance.
It's up to the instance operators. Lemmy.ml just announced proactive defederation. Some others should follow suit. You as a user can switch instances or operate your own, giving you full control.
Mostly yes though sometimes there are bugs where it doesn't work generally speaking you should be able to follow and comment on a kbin instance no different than lemmy