You ignored my previous suggestion that you separate Posts and Topics – that might be important for a ‘normal’ database.
And include the date of a post – essential, no?
And several categories instead of only a boolean IsMeta (etc.).
One good thing about the current Posts structure (i.e. with ParentId which is presumably a reference to another Post) is it would support an n-level tree of posts – instead of only 2-level i.e. “topics contain posts”. Is that good though, and done on purpose?