How many gigs of RAM do I need for this game? 64? 256? 4096?

The game takes 2.5 GB of RAM once started. It uses more when you leave the map screen and menus and actually start playing. It was hovering around 4 GB of RAM for my yesterday. That's the game alone.

Well, doubling is probably going to be more than you actually need. That's why it's a rule of thumb.

4GB - system OS, antivirus, **** torrent, Redditside.
16GB - all raw game assets.
XXGB - game optimization constructs.

Now, you probably don't need all 16GB for the raw game, as things like intro movies or localized audio don't necessarily need to be loaded. And depending on how much the game expands to make loading/processing/reference easier, the 'extra' GB might be very small, or very large in comparison to the raw assets. It's very, very unlikely they will be more than double the raw though.