dont use any sony store, when you want cfw. you can also create your own psx eboots with adrenalin and open the complete psx world for you. even the store dont have all games listed. just download a copy somewhere from a rom site put it in adrenalin and all is fine.
the original sony vita memory card is the best what is working, but 8gb is of course tiny. but psx eboots are mostly 50% smaler in file size, instead of a image ISO. FF CC and Suikoden are maybe ~2,5 gb together. pro tip, let 4 gb free space on your memory card. FF is big since all 4 discs are compiled into one eboot file.
offtopic :
I am search a PSX Eboot for the X-Files, all 4 discs need to compiled, but there is no pirated copy on the internet that work on this way. has someone a solution ?