Can you SLI in Aster? And more importantly, how does it work?

I want to buy another GTX 970 to SLI, but I'm not too sure how to go about this since I've never done this before.

Will Aster get confused if both people are gaming?
Does SLI kick in when only one user is playing? Or is it already running from the start?
How many monitors can I set up with two 970s? Will it get confused on how I want it assigned or will Aster still recognize my system as two separate GPUs, but can operate as one.

I really want to be safe about this before I decide to jump the gun and immediately buy one.

Thanks to those who can help! 😀