Different users will prefer Roon or not. It’s worth a trial IMO. In the trial, try to use it extensively, as there is a learning curve. Roon’s at its best for finding music related to what you already like and for providing tons of metadata for a lot of music (but not all). It’s at its worst for classical music. Since Roon has no conception of what a sonata is, or a string quartet, you might imagine it has trouble finding those things, and you’d be right.
As to connecting the DAC straight to the computer by USB, that’s often possible. However, not if the computer is in the other room, for example. I don’t think it’s a general rule, but I have had better results -- fewer noise problems -- when using a network-attached streamer (such as the Node) and then to a DAC rather than a direct USB connection from computer to DAC.