Based on my experience so far, new posts using the hashtags tracked will show up on the microblog. Old posts aren't going to get picked up.
All fedi accounts should be able to comment and participate. However kbin infra rn means even if you follow this magazine from your client logged in from another platform (especially masto builds), the content will not be fetched.
However, if you follow a kbin user account, their activity will be fetched and it'll show up on your timeline. So, that's a pickle i can't resolve technically and looks like any workarounds will be up to your browsing taste.