The 12GB PS3 is exactly that, the flash memory on it is actually 16GB, but the OS stuff and formatting uses 4GB, so you actually get 12GB to yourself, as in, you DO get 12GB, unlike other models that state like 320GB but you only get 300GB after formatting, here, for some reason, they advertise the amount AFTER all the OS stuff and formatting.
And yes, GTAV will work fine from disc, there's an 8GB Required install, and if you get any DLC, luckily, the first batch is Disc Locked Content (BOO!), so DLC only requires 100kb unlock Keys.
edit: And just to mention, you CAN'T use a flash drive or any other USB External drives to store content with a PS3, that option is only available on the Xbox 360 since they don't allow you to use normal hard drives.
Edited by Ash_735, 08 September 2013 - 03:21 PM.