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First of all, very interesting concept, I'm on board. While it's not that small, having the I/O on the bottom and the radiator at the back just gives such a nice look at all the components, and I really like that.So onto my suggestions:The radiator seems to define the size of the case right now, but you also need quite a bit of room for angled cables on the bottom. It could make sense to recess all hardware (except the radiator) upwards into the case to allow for more space for the cables underneath. That way, you wont have to make extraordinarily tall feet, will use the currently wasted space at the top of the case and can create passive exhaust vents that are neatly hidden inside.To me, vents in the acrylic kind of kill the look, maybe you could flip the PSU around and let it intake from the inside? That would help you solve the exhaust problem, too.In terms of case feet, I'm thinking of a piece of very thick acrylic (15mm or so) that is flush with the two opaque side panels but recessed from the two transparent ones by 20mm or more, letting the case look like its levitating. There would be a cutout in this sheet to allow I/O cables to be plugged in, and it would have a channel running to the back to hide all the cables coming from there. I see that this might not fully work with the way the GPU is positioned, but it could be worth a thought. That acrylic could also be transparent, smoked, and lit with LED to get a bit illumination going.As you'll have to use relatively tall feet, positioning the case button on the bottom seems like the best idea. Would work nicely with idea 3 I guess you're going to glue the three acrylic panels together? Try to find out how to make this look as seamless as possible to show of the components a bit better. Ideally, that part of the case would be a single part, but I understand that's impossible to implement.There's a lot of space next to the pump, maybe you can use that to fit "standing" SSDs there? So they would only be attached with two screws through the back of the motherboard tray.
First of all, very interesting concept, I'm on board. While it's not that small, having the I/O on the bottom and the radiator at the back just gives such a nice look at all the components, and I really like that.
So onto my suggestions: