When you block someone, can they still reply on your forums/ and find your forums?

Yes they can still post, as long as they don't try to speak to you directly

Pretty sure they can't enter your threads, because you can't enter those of someone you've blocked. You get a blank page with:

i'm pretty sure blocking someone just means you can't see their forum topics or posts, not the other way around. you can't control what other users can and can't see. however, they are not allowed to respond to you directly; i believe if they try to ping to you they will get an error message stating that you have them blocked, and they can't try to address to you without pinging you because you can't see their posts anyway.

I personally always found it kind of stupid that you can't view the entire topic by someone who you have blocked or vice versa and that there's no way to just... block that specific post or who made it but you still see the content if it happens to be the start of a thread. Re: event threads, site feedback, that sort of thing.

I know it already kind of breaks the "You block, no contact EVER AGAIN" rule but it's still stupid when you lose entire posts that you sometimes need to be involved in.

If you have the person blocked, you can't see their posts. If they have you blocked, you can still see their posts.