The terminal will of course not be supported by Rockwell Automation if you put third-party components into it. The RAM module is not proprietary, but the BIOS probably has a narrow set of compatibility.
The removable CF card can be any brand. I recommend "MLC" type cards because they have longer write lives and higher temperature ratings than conventional cards. The card should be under 32 GB and formatted for FAT16.
The internal CF card (on old pre-v6 terminals that use one) is formatted with several different partitions that contain the operating system and other components. You can duplicate them with a Linux computer and the "dd" command, but I have not used any Windows-based disk image duplicators on them.