I have made this transition about 10 years ago and it went very smooth.
I am not sure if this will be of any help but you can setup the ethernet backbone first. What I mean is run all your wires, install the switch (if you don’t have one), connect to your existing LAN/WAN. Next, take one PC, put your ethernet card in, ensure it is communicating will all other PCs. Once you have established that, one PC at a time, make the transition. Remember you must start at the end route as you need termination.
I hope this helps in some way.
Let me know if you have any more questions or if I am even in the ball park of what you are asking.