I think right angle cables would make all the difference and save valuable space within the case. A right angle SMA cable would let you scoot the SDR to almost the bottom of the case.

https://www.amazon.com/dp/B07VKRKGWV/

Then a short right (or left) angle usb extension would probably fit within the case.

https://www.amazon.com/dp/B079GV7FXT/

I love the idea of a portable all-in-one device. You could make it powered by PoE and you’d just need to plug in a network cable and antenna and you’d be set. Great job!