Never had SFF stuff until recently, but the reasons why I do it are the following:
Inkscape can't handle the number of objects needed to do an ATX case, and my workflow depends heavily on it (hell, it can't even handle vent holes sometimes!
Material costs are a bit much with anything large
Why...
By now, it would be a rather decent idea to configure something like the Corsair One with the PSU at bottom, a large fan at the top blowing air down at the GPU and heatsink.
Something else to consider would be having very tall feet, which *might* help with airflow. Partitions/air ducts would...
The bottom fan is a bit of a weird one for me because it's going to be cannibalized by everything (@tinyitx 's concern), and a lot of it will be exhausted directly by the side fans.
Perhaps flip the whole thing such that the PSU is at the bottom? I can see issues with the top mount causing...
What is a focus of your projects (design wise)? Also, what are some of your other interests?
(since i do science and the purpose was efficiency here i am)
temporary could be cc design works? i'm not very creative :P