You are right about the graphics card, it would be redundant on a node for Corona, so you can go with onboard graphics or a low end card (just in case you ever need to plug in a monitor to work on the machine directly vs. accessing it remotely from the main workstation).
However, memory would not be redundant - nodes are best to have the same memory as the main machine if possible, as otherwise something might render on the main machine but not on the nodes because they run out of RAM. Nothing will "break" in the technical sense, DR and Backburner will still work if nodes have different amounts of memory, but if you try and render a scene that needs 64 Gb of RAM and your nodes only have 8, then they will run out of memory and contribute nothing to the networked rendering.
I do have 64 Gb on my main system, and 16 Gb on my nodes, but I don't render any heavy scenes so that works for me as all my renders need less than 16Gb so I am fine. That is likely pretty rare though, especially if doing any full-scale arch-viz work for example :)