So what CPU did you get?I recently got one of those. Or rather the Intertech IM-1 Pocket naming of that. Was a bit tricky to get, ordered it from a co.uk address but it was shipped from NL or DE.
Must do a proper review, but I'm using with a full ATX power supply which is one of the reasons I chose the Asus TUF Gaming B500M Plus: it has the x16 PCIe slot one slot down which means that even with a full size PSU I get the full length GPU options which otherwise is only possible with SFX. Main reason I wanted mATX is due to the 4 DIMMs and extra PCIe slots so in the future I could add more M.2 even if I might have to run some at x1.
It's been years since I had a smaller case (I was on my Intel Ivy Bridge 3570K for nearly a decade). My previous case was AeroCool DS-200 which is a Define clone type thing. Got it cheap from Amazon warehouse some time: favourite feature of that was the case fan controller had a 0/1/2/3 so it could turn them off which was nice. Least favourite thing was a lot of the plastic is covered in this slip-proof rubberised finish is I was never able to clean without it becoming sticky. Horrible stuff. Still it was 65 litres.
For the new IM-0, the mechanical 3.5" drives had to go though: in theory there's space at the top for one and one more at the bottom (as you may know this case is almost entirely symmetrical and top and bottom covers can be swapped around).
In practice the bottom one is just far to close the GPU (if you're using SFX and a GPU in the top slot this would be less of an issue), and the top one blocks the best route out for warm air. Back only has space for a 80mm case fan, so after removing the 3.5" drives, I put a 120mm on the top. A second exit fan at the top would need to very thin when using an ATX supply.
SATA cables at the edge of the board (like this Asus I'm using) are very tight so might have to take out the bottom "traverse rail" thing. Also, I have placed some 270° SATA ("left angle") data cables in my ebay basket and might buy those as the 2.5" at the front really don't have much space for the cable. With a spacer it might be possible to place any 2.5" drives at the front in front of the case - doing away with the need for a 270° SATA leads - but I might place a fan there instead.
The new case is definitely louder than my previous 65 litre monster case. Maybe I was being greedy to go for a 22 litre case. A few more litres and things would be a lot less tight.