Iken is not an easy mission to stay financially solvent and also have a city standing at the end. I finished it fairly recently, and even though (or perhaps because) I stayed within my personal rules as much as possible, it's probably the worst city I've built on Very Hard because of the money and map layout.
For me, the best way to defend my city was to concentrate most of the housing in the first part of the game on the two central islands, since land attacks couldn't come from there. I put a house on the mainland to staff the ferry so I could trade by land and buy wood to defend the water, and I prayed that the Kushites would not attack the south-east island (they didn't). This is not the only way to deal with the city, but it worked for me. If you do a search on "Iken" in the forum, you can see how others have managed the situation. A good thread for this mission is iken at very hard level. You can also look at Brugle's design plan for the city in Icky Iken, which may help give city design ideas. Also, be sure to look in the Downloads section to see how others have done it.
“If I could stand wearing an Eagles jersey, I would try to get an old-school Eagles jersey made up with "QB Eagles-0". I think I managed to find the only way to make a football jersey geeky, but there you go.”
-Paul Mazukiewicz
My nation of One-Ballia at NationStates