IMO the Node 2(i) is one of the best-bang-for-buck HiFi products around.
I agree with those who suggest just using it for a while before investing in fancy cords or cables. I do prefer it wired (ethernet) to WiFi, but especially if you have fairly fast internet service, WiFi might work fine for you.
I also agree that instead of buying a stand-alone DAC to use with the Node 2, you might want to wait until you are ready to upgrade the whole shebang. Any of several integrated DAC/streamer/preamp products at around $3K would offer a nice one-shot upgrade. The Matrix Element X, iFi Pro iDSD, or a used Auralic Vega G1 would deliver USB and balanced outputs along with any improvements to the DAC.