OK so your external card needs to be fat32, you can put the rom on your internal and flash it that way, but just make sure you don't wipe you're internal sd card because the room file will get erased.
As for Cyanogen 10, there's a ROM in the development section that you can use. I use it as a DD and it runs great.
Sent from my LG-E980 using xda app-developers app
Future Phone: LG Google Nexus 5
Current Phones: Samsung Galaxy Note 3 AT&T[Rooted], LG Optimus G Pro AT&T[Liquid Smooth]
Past: LG Optimus G AT&T, LG Google Nexus 4, Samsung Galaxy S3 AT&T, Samsung GS2 AT&T, Sony Xperia ion AT&T, Samsung Infuse AT&T(First Android Phone), All iPhones before that.