Ram is pretty much dirt cheap.
16GB is probably plenty, but I went with 32GB which wasn't really all that much of a price difference.

Since you have an SSD in your build, a RamDrive isn't going to add that much more speed.
So there probably isn't any reason to go for 64GB of ram.

I personally have two SSDs in Raid 0, which is very nice.
I'm not saying one SSD is not good enough, but striped... they're that much faster.
Which is an option, depending on your budget.

I'd probably go with one drive for the Operating System.
A different drive for the gaming folder, sized to accommodate each game that you'd like to be playing.
If you're going to record your play, to make movies then another drive for that.

A single big video card is generally best for boxing.
If you're running a lot of clients, on higher settings, that is often the bottleneck before CPU or system Ram.
The number of monitors you'd like to use, is going to be determined by which video card/cards you go with.