Yes you can connect two monitors simultaneously and extend the desktop to the second monitor.
Yes you can connect a 500GB mSATA disk and use it as your boot drive.* (I am writing this reply on a NUC using exactly that configuration right now.)
* Note that using a 500GB mSATA drive is an expensive way to go. If you get the "H" model NUC with room inside for a second drive, it might be less money to buy a smaller mSATA drive as your boot disk, then get a 1TB spinning drive as a separate data disk.
Thanks for the answer.
Adittional question :
Is an mSATA SSD disk not faster or more performant than a "standaard" SATA SSD ?
I can't speak to the universe of SSDs, but when I was deciding between the Crucial m550 SSD in its SATA and mSATA forms, they had the same read/write specs.
Obviously if you intend to get the smaller SSD and a second data drive, go for the mSATA SSD.
The mSATA can reach the same speed as SSDs depending on the manufacture specifications but the biggest different is the form factor.
Here is a very informative link:
NOTE: These links are being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.