4GB should be fine, IIRC it's the lowest size that the Mark 1 empegs shipped with.

Two things to address that I can see from the photos and process that has been done so far:

1. Add a jumper on the CF adapter to set it to master, if the CF card is going to be the only drive.
2. Download and apply the Disk Builder upgrade from here: http://www.empeg.com/downloads
Detailed instructions on using the disk builder can be found in Tony's drive upgrade FAQ starting at step 6. http://www.riocar.org/modules.php?op=modload&name=Drive_Upgrade&file=index