To my knowledge, unfortunately, you cannot add houses or population to the cities via game events. You can only add industries.
As to create a map on a random island, I would advise thinking like this:
1. what resources would the island have to offer - these would be demands in the ports
2. what does the island need - these would be what the ports have to supply
3. then consider what kind of game you want - competition/one company only, modern/19th century, etc..
Say you will play it as cold, far away, island (as it is). Then it will obviously need produce, meat, grain, clothing and goods. It could have uranium mines inland and a lot of wood - these would be exports. Throw in some milk farms and you would have a complete economic system for an island of that sort.
Of course, you could make up a completely different economy - different imports/exports. But I usually go this way, so that's my advice.