There won’t be a need for the graphics card if you use a current desktop cpu from Intel. Current versions of QuickSync will outperform discrete GPU cards.
If you have a separate hard drive or SSD, you could connect it to the old server. Then move the Plex data folder onto it in preparation. HowTo: [HowTo] An extended guide on how to move the Plex data folder on Windows
Save the registry branch for Plex Server: https://support.plex.tv/articles/201539237-backing-up-plex-media-server-data/
Write down the current drive letter for each of your media drives.
When you connect them to the new system, restore them exactly as they were.
Install Plex Server.
Test it with a small library.
Shut down the server.
Then connect the separate drive with the Plex data folder on it.
Give it the exact same drive letter it had before.
Import the saved registry settings.
Shut down the old machine and never start it up again.
