hrvoje_hr all the columns ending with
_count will be computed text time a post is created or deleted in the discussion, so if you are not able to update them in your migration, they will be updated next time someone post in them. Same for the user
An extension could be created to re-compute all of them, but I don't think it has been made at this time.
post_number_index column tells which
number should be used for the next post. That column is important and should contain the highest post number value (next post will be that value + 1). That column must be updated in order to not run into errors of duplicate post numbers.
The value can be higher than the number of posts, if some posts were deleted and some post numbers are now missing. It needs to be the highest number value (or bigger, it won't create issues).
Again, an extension could be written to fix discussions automatically for that as well.