Dear god. I hope these are joke posts.
Any cable that can give you a solid Gig E connection is perfectly fine. The only reason to ever run fiber is for ethernet runs over 100 meters or in EXTREMELY EMI noisy areas (think radio rooms or sitting right next to a wave guide for a satcom link).
The layer 4 (TCP) handles the buffering and makes sure that the packets are complete when they get to higher levels of the network stack. Anyone who tells you anything different is trying to sell you something that you don’t need or doesn’t understand how networking works from the physical layer all the way up to application layer.
(And yes RAAT uses TCP now - see the release notes for build 234: Roon 1.3 (Build 234) Is Live!)
Save your money. Un-shielded twisted pair cables from Cable to Go or anywhere else are perfectly fine. “Audiophile” grade cables for digital signals are snake oil.
For CD quality - Fast Ethernet is fine.
For Hi-Res - Go with Gig E.
Unless you are saturating a Gig E switch (HIGHLY unlikely), you will be fine using a switch. And there is no need for a LAN isolator.