It's this true? Curious because almost all cases have exhaust fans towards the top. Asking because I wanna find the optimal fan configuration.
The reason for the usual upward flow of air is that ATX, and microATX (not sure about mini ITX) were designed for an airflow moving from the bottom (usually at the front) up toward the top rear. Originally they intended for CPU's to have passive heat sinks and the fan on the PSU to provide the air for the CPU. As CPU's got more powerful this was no longer viable but the practice continues.
Linus Tech Tips ran an experiment of three pc's not cleaned out but running for a whole year. The conclusion was more-or-less, balance your air in and air out (have a slight +ve airflow just to keep dust out of holes without fans), and the bottom exhaust to blow dust away, as well, bottom intake picks up dust. It also means the PSU won't suck up dust if it's fan is in the bottom. Also, filter any intake fans, don't filter exhaust fans.
In your case, the motherboard could be orientated in so many ways, and the GPU will likely need to be fitted to a riser, the PSU will probably be in an odd position too, and well, it's cylindrical. It's almost guaranteed that your airflow will already be different from a typical case.
Now in regards to strength of convection. When have you held your hand above something hot and felt a gust of air going up? I bet never. Sure hot air might be able to hold up paper, and in the great outdoors some birds, and blimps, may be able to utilise upward flows of hot air to gain altitude, but vs. a fan convection, at least at the temperatures your PC should keep it's air at, isn't going to be anywhere near as strong as the fans forcing air around. Passive cases don't have the benefit of fans, hence why they are designed to utilise convection.
You will have to look how space works out in your case, but it may be entirely viable to fit some sort of water cooling setup in your case using a reservoir, or potentially even evaporative cooling (I personally don't know how effective it is, I just know it exists and is sometimes used). Your components aren't circular so you will end up with gaps which could be used for either things such as that, or cable management.
