What on earth do you do for optical drives
That's easy for such a case... use an external drive that can easily sit on the desktop. I use a Samsung portable with my 11" laptop, which is USB powered and does okay at both reading and writing. However, I do prefer dual optical drives that are internally mounted for my main rig... can save alot of time copying files to HDD for later burning, etc.
As for small and useless.... getting "toasty", Corsair liquid cooling is quite effective and would do a good job at keeping components cool in this case, and given there are 3 mounting places for liquid cooling, one unit could be assigned to the CPU and dual GPUs respectively, thus cooling the 3 hottest components quite well.
Having said that, I would not use this case as a main PC, rather as a guest or backup PC that serves to surf the net, create documents, etc... nothing that's resource intensive, and I certainly wouldn't install high-end components in it as I have all that in my main rig, and thus it would not need power to burn.
I haven't thought about water cooling. Never needed it before, so not really sure what I would get out of it now.
As John pointed out above, the unit in the screenshots is Corsair liquid cooling, not water cooling, which are sealed units and thus makes them safer around PC components. I have one in my main rig and find it better than air cooling, hence I would be inclined to go with liquid cooling in a smaller case such as this one. It wouldn't be essential but recommended, especially if you are going with higher end CPU and GPUs for gaming.