If we break the 'City' into districts that might help. Then people can pick what kind of district they want to work on.
I was thinking it would be good to do that too - not only to break the build up into a few different focal points, but also to allow a bit more variety, because the different districts could easily then take on a different look, and still look like they are part of the same build.
Different levels could work nicely. They wouldn't even have to necessarily be one level below another, they could radiate out like spokes on a wheel but at different heights depending on class.
So here's my idea -
There could be a centre large island that has the large industrial buildings and machinery - forming the industrial heart of the world - with the smaller islands around it, which would be the more residential areas of the world.
Upperclass ones would be above the ground level of the industrial section, and have fancier looking buildings, more landscaping/gardens and decorations for example. There could even be a couple of small islands that are parks... stuff like that.
Middleclass would be below the level of the Industrial section. Perhaps have the houses more tightly packed together, and smaller and less fancy, less gardens and landscaping.
We would have to decide if the outlying islands connect to the centre one or not. Perhaps not, and we can add a couple of smallish airships to show how people travel around. Though I think it could be nice to have some smaller islands connected with arched bridges in the districts.... maybe having each district separated from the main industrial section by a reasonable distance but those districts being made up of a cluster of islands that are closer together and some connect.
We could have the slums directly below the central industrial part. As the people living there work in the factories above, so it's easier to get to work, and they can't afford airships to get to the other districts, so have to live where they can get to the city.... an it's the dark (on account of the city above blocking the sun) and uninspiring part - so would be very slummy. Perhaps as an upside down city - so you've got the buildings coming down from the ground that the city above is on (like a stalactite, only squarer), with some interconnecting bridges and stuff to make it look interesting. We could make hanging lights to light that underneath area (so you can see everything) by using fenceposts as the cable, and glowstone as the "bulbs" - which would also soften the look of that underground area, and almost take on the look of roots or something hanging down from the land above.