Hi, @proofofbrainio.
I see this is a new community / project and it seems to me to be very interesting. From now on, I'm gonna use the proofofbrain tag in all my posts (by the way, I just did that in my most recent post).
So, initially, I made a delegation of 250 HP to see how things will work (and I can increase it later, depending on the results).
Question: Do I have to use proofofbrain.io to post, upvote and / or interact in order to receive my rewards in POB?
No, using the tag or interacting with posts with the tag is sufficient, but you will probably find that you get more POB upvotes when posting from proofofbrain.io.