@lynx29
Mini-itx is a topic up my alley I love small builds. I owned the Raijintek Metis and I do agree with the
@tabascosauz the cooling for the case is not that optimal. The case don't really have clean traditional airflow like normal tower cases with an intake fan infront exhausting all behind or the top. The power supply is located at the front of the motherboard a design to decision to make it as compact as possible yet retaining full gpu compatibility and full height air cooler compatibility. Despite the airflow flaws, it can be remedied well with mods. I still highly recommend the Metis as it is a no compromise case for full size hardware and cooling. It is basically at the limits of full size hardware. I could cool my cpu with a massive Noctua d15s in this case 160mm high. Even despite being itx I have cooling capacity of a near mid tower case. You can gpu up to 26cm long here provided you use an sfx psu, short atx works too but not recommended. You are building in a case with only 13 litres of volume and the space is real tight. Volume wise its similar to an ncase m1 though the layout is different and with a much cheaper price.
For power supply always go SFX even if the case support atx always use sfx with a bracket. It really really make it alot easier to assemble rather than trying to jam a full size atx psu in. I have enough of atx psu and I would not buy another one now. Sfx psu have really improve in quality versus back then where the only player was Silverstone. I used a silverstone 600w gold before on paper it sounds good but in practice its not good as it is not reliable and prone to dying, also the voltage is not stable I changed two of them. User reviews for it reflect it too. The sfx gold standard now is the corsair Sf series. I am using an sf450 platinum now, super solid psu, the fan never even spin up at all and voltage is super stable rivaling even atx psu based on jonnyguru reviews. Plus the 7 years warranty is awesome add to it and the braided cables.
Regarding sandwich style case where the motherboard in one compartment and the gpu in another like the dan a4 I posted in my page back allows you to go even smaller. There is an advantage of sandwich style allowing better cooling than traditional cases and the hot air from the gpu and cpu is not mixing together. The downside is of course the cooler size is very short negating the split chamber design.