So there are multiple approaches to pre-paring an Workbench for your V4. You can use another Amiga or WinUAE to build a basic installation along with the drivers for all the cool V4 hardware (network and RTG). The network driver is being polished right now and already looks pretty speedy (certainly faster than on the V2).
You can also buy a pre-installed WB on a CF from Cloanto but there isn't really any benefit to this apart from the convenience of having a pre-installed environment. You still need to add the SAGA drivers to that image.
Our current plan is to provide a free AROS based image for all V4 owners. This is pre-installed and tuned exactly to the V4. It is currently a WIP but it already looks to be a great alternative to the traditional workbench. In addition to being fine tuned to the Vampire's hardware it also has networking and many other features built in. Check Pedro Cotters channel if you are interested in the progress.
I personally just used an A1200 with a CDROM to install WB 3.9, MUI, Roadshow and iBrowse. Once the SAGA drivers are installed, it is easy enough to download anything else you need. But I will soon switch to AROS full time because it is just simply better.
If you have trouble getting it going, drop us a line here. Or we are available on IRC (Freenode has an #apollo-team channel) or on slack.com.