Good day LiSchill,

One CSV-3202(H) USB3.0 to 4K adapter will use the full bandwidth of a USB3.0 port, when it is set to 3840 x 2160 at 30Hz. You cannot put it at 60Hz because that will not fit. 
If i am not mistaking you have 2 x USB3.0 ports on your Lenovo AIO. So you could connect 2 times a CSV-3202(H) to each of the USB3.0 ports and connect 4K screens to that as long as those screen can run 4K in 30Hz.
Connecting an MST Hub to a DP output on a USB-to-DP Graphics adapter wont help you, because you are already using up the complete bandwidth of the USB3.0 port by connecting 1 x 4K screen at 30Hz.
Having said all this, please take note of the fact that the USB Graphics devices still rely on the Grpahics Card of the system to make the Video signal available to the USB ports. We did not test with a GT820 but i would think it has limited capacity in this context. I am confident you could add 1 4K screen, not so sure about a second 4K screen, and i seriously doubt if you could add a third 4K screen. But this is just an educated guess.