1) goods will be needed as with the other settlements - at least the goods are already in the game files...If there's units, there's definitely going to be a military component here. Perhaps the Egyptian settlement produces units instead of goods, and goods are obtained by fighting with these units? I don't see it being possible to balance any sort of combat if we aren't actually using the units ourselves, since there are far too many variables to account for when every unit is available for use. On that note, I don't think GBs should be factored in, either. They don't provide a benefit to the Vikings or Japanese settlement either, after all.
2) if we produce Egyptian units, maybe we will get more space to work with to accommodate for extra military building?
3) the difficulty indicators also make me think of the possibility that you fight with your own troops and that you can choose a difficulty that suits your GBs... In that case I would expect that you can get 10-20% more rewards for the more difficult battles