MaybeSo,
That last missing space was probably just a copy/paste error. If you see his first post, the 'to' and 'gather' are on separate lines. Probably were joined when he tried to correct the formatting for the 2nd post.
I disagree about the term auditorium not being used often. In this case, congregation wouldn't be used as that term refers to the individual congregations that attend a single kingdom hall. They could have just used the term 'kingdom hall' without adding auditorium, but the usage of auditorium narrows down certain sentences. If they said kingdom hall capacity instead of 'auditorium capacity', this could be mistaken to mean that they would be including the capacity of secondary rooms (2nd and 3rd school rooms) when determining whether or not a kingdom hall was being used fully.
I think this letter is legit. Consolidation is already happening in Australia (reported by news) and some parts of the US (reported on this site). They probably felt a need to send a letter to put their spin on it before the rumor mill took over.