I'm about as new to knowing about the flash memory as you are...

Probably not the best one to ask... Although, from reading the manual and looking on the net, I guess you can use the Compact Flash (with PC Card adapter) to load patches and samples and stuff onto it...
The internal expandable RAM (up to 512 mb for my Fantom XR) gets wiped when you reboot. The onboard 16 MB of memory (again, for the Fantom XR) will retain any data placed into it, since it's like flash memory too.
As far as Roland is concerned (I confirmed this with a Roland rep in Toronto) the max is 1 GB. However, there are people that say 2 GB works as well.