ROCK is based on Linux and uses either USB audio drivers for certain DACs and USB controllers that are released for the Linux kernel and are part of the install.of the distro. In the case of ROCK it’s a locked down OS so will only support what is available at time of building the specifc version of ROCsk. So if the DAC has good Linux support then it’s likely it will work ok, if the manufacturer don’t release drivers in to the Linux world then sometimes DACs will work fine but won’t have the full feature set available as they will use veneris USB Audio or USB Audio 2 drivers for the chipset. So you might get limited DSD support as an example.
There a fors and against using DAC connected to the core , only you can decide if it’s fine as it’s your ears, the DAC maybe immune to the unwanted RFI that the core may generate.
Not really. But, trust your ears, whichever sounds better to you.
ROCK is a closed system and you will not be able to install anything. The main issue that people run into is that Native DSD and Linux can be spotty, but, since Henry mentioned that the D50 works fine that way, so you should be good to go.
Give it a try is the best way! And come back and ask, we are friendly fellow users around here.