I am hearing that the horde on The Forgotten Coast realm will not report census, at least to warcraftrealms, and reporting numbers seem to verify this. What lvl horde would I have to create in order to report? Again, why can't allies report horde numbers? and visa versa?
CensusPlus uses /who command in-game and that only returns your own faction. There is no possible way to Census "the other faction" than the toon you have logged in.
Fuxie already covered your questions, but I am going to give you an additional pointer for the possibility that you create a level 1 alt on the Horde side. If you only have time for a single census per day on the "other side", try to time it to about 20-21 hours server time. That way you are more likely to get higher numbers with a single pass.