How to remove post completely?

[Canapin (Coin-coin le Canapin)]

In understand that you probably want to do that from the interface, but as a safe alternative,

If I want to completely delete a post, I should just hide them?

Hard deleting a post using .destroy is the recommended way. I will not break stuff in Discourse, there are jobs that ensure consistency. There may be some inconsistency in counts for 1 to 7 days depending. (Sam made 9997 posts but REALLY he only made 9996 posts)