In respect to this, do you need a roon core?
Every Roon set-up requires a Roon Core. It's the conductor of your music streaming orchestra. It could also be a NAS drive or a dedicated music server (such as Roon's own Roon Nucleus) which is pre-installed or installable with the Roon Core server software.
One may also ask, is Roon worth the money? From what you describe, the advanced playback features (separate streams to multiple endpoints) might not be what you need. But if you just want something to play tracks in your local system, Roon isn't worth the money.
In respect to this, does Roon improve sound quality?
Roon is built from the ground-up to produce extremely high-quality output, however Roon works differently from other software, so you may not be able to drop it into an existing setup and get the same results immediately.
What do you need to run Roon?
Roon is software, so you'll need hardware to run it on. You can run it on a headless (no display needed) Mac or a PC, or you can set it up on a high-end NAS box (Roon recommends having at least an Intel Core i3 Ivy Bridge-architecture CPU, 4GB of RAM, and an SSD to run the server software).
