As for graphics card, a CyberVision 64 will be a good choice, since it has a build in monitor switcher, so you can just connect a loop cable from the A3000 scandoubler to the extra port on the CyberVision 64 graphics card. From then on, it's auto switching between screen modes, so no need to have a manual switchbox or a dual monitor setup. The card comes with 2 or 4 MB rtg memory. 2 MB will be an improvement over native Amiga video output, while 4 MB is the max graphics memory you can get with a Zorro graphics card.
As for ethernet cards, there a lot of good choice out there; X-Surf and Ariadne are the most common ethernet cards. Useful for connecting to the internet, FTP sites and Samba networking, but would be a bit of waste "just" for file transfering if you connect a SCSI CD drive to the computer.
