Resident Evil: The Mercenaries 3D eShop download is 4714 blocks. Hehe, there is nowhere that seems to state that plainly and so obviously, any search for that info should direct here ^_^
There's no demo for Resident Evil: Revelations as there was on the original cartridge, but it's available as a free download from the Nintendo eShop anyway. The options are New Game or Continue, so there appears to be only one save file, and it also appears to be deletable! Good news there.