Bonus points if you set up pumps either end so the canals actually flow (although it would massively increase the risk of flooding)
For crafting ideas - recently I've tried to set up forts dedicated to the crafts I usually ignore:
* Clothing industry is good fun, especially if you aim to only use dyed cloth. Dimple Cups underground (for dye) + Rope Reed overground (for thread) is a combination you can use all year, or if you're going fully underground then pig tails (for thread), but they only grow in spring and summer. Silk is also an option if you don't mind braving the caverns.
* Clear Glass industry is good if you use magma glass furnaces and magma kilns, otherwise it just takes too much wood. Green glass is easier but less interesting and less valuable. You'd probably need to move magma up, too, if you didn't want to be hauling sand all the way down from (near) the surface.
* Soap is a really challenging one - you need a good supply of animal fat to make the tallow so having lots of livestock is important. Might be fun with the genetic traits in the new version to try to breed animals with lots of fat. This would combine well with leatherworking and bonecrafting, and you'd have good meat supplies.
I think clothing would be a good choice if you're going for Venice-style: if it's flowing water you could have your dye mills powered by waterwheel, and irrigation won't be a problem with all that water around.